University  of  California  •  Berkeley 


WIRELESS  COURSE 


in  Twenty  Lessons  by 

^*C\&^?ite^  *^ 


TH 


Published  by 

ELECTRO  IMPORTING  CO 


NEW  YORK 
Lesson  Number  One 
THE    PRINCIPLES  OF  ELECTRICITY. 

^iiN  the  study  of  wireless  telegraphy,  many  electrical  terms 
fl|  and  instruments  are  encountered,  making  it  necessary 
for  the  beginners  to  obtain  a  working  knowledge  of  elec- 
tricity before  invading  the  more  difficult  subject  of  wireless. 
We  have  therefore  devoted  the  first,  second  and  third  lessons  to 
a  concise  and  practical  course  in  elementary  electricity.  We 
do  not  claim  that  it  is  complete,  inasmuch  as  our  course  only 
covers  electricity  in  general  to  give  the  student  a  better  under- 
standing of  wireless  telegraphy.  For  a  better  knoivledge  of 
electricity,  we  recommend  the  reader  to  the  many  excellent  text  books  which 
cover  the  subject  in  a  thorough  manner. 

Electricity  in  its  simplest  form  was  known  to  the  ancients  many  cen- 
turies before  the  Christian  era.  Thales,  of  Miletus,  a  city  of  Asia  Minor,  in 
the  seventh  century  B.  C.,  described  the  remarkable  property  of  attraction 
and  repulsion  which  amber  possesses  when  rubbed.  When  being  thus  rubbed 
he  found  that  it  would  attract  particles  of  dust,  dry  leaves,  straws,  etc.  This 
phenomenon  was  noted  from  time  to  time  in  the  succeeding  centuries,  but  it 
was  not  until  1600  A.  D.,  that  Dr.  Gilbert  of  Colchester,  England,  took  up 
the  study  of  this  subject.  Because  of  the  thoroughness  with  which  he  delved 
into  the  study  of  electricity,  he  is  considered  as  the  founder  of  the  science  of 
electricity.  He  gave  the  name  of  electricity  to  the  peculiar  force,  which  he 
derived  from  the  Greek  name  "Elektron,"  meaning  Amber. 

Electricity  is  found  in  two  forms,  in  one  it  exists  as  a  charge  upon  a 
body,  and  is  known  a?  static  electricity,  while  in  the  othes  form  it  consists 
of  a  moving  current  through  a  wire,  known  as  dynamic  electricity.  We  there- 
fore have : 

Electrostatic  electricity,  that  branch  of  the  science  which  treats  with 
electricity  at  rest. 

Electrodynamic  electricity,  that  branch  of  the  science  which  treats  with 
electricity  in  motion. 

If  a  glass  rod  is  rubbed  with  a  silk  handerchief  and  brought  near  a  small 
pith  ball,  (made  of  dry  flowers),  which  has  been  suspended  by  a  silk  thread, 
there  will  be  an  attraction  of  the  pith  ball  towards  the  rod.  However,  as 
soon  as  the  pith  ball  touches  the  rod,  another  action  takes  place:  the  ball 

Copyright  1912  by  K.   I.  Co. 


2  WIRELESS  COURSE— LESSON  NO.  1 

being  repelled  from  the  rod.  The  explanation  is. that  the  ball  originally  held 
a  charge  opposite  to  that  held  by  the  rod,  the  charge  being  neutralized  on 
touching  the  rod,  and  the  surplus  charge  of  the  rod  being  carried  on  to  the 
pith  ball.  Being  that  both  the  same  charges  exist  on  the  ball  and  the  rod, 
both  will  repel  each  other. 

Two  kinds  of  electricity  are  produced  by  friction,  the  kind  of  charge 
being  dependent  on  the  substances  rubbed  together.  Thus  if  glass  is  rubbed 
with  silk  it  becomes  charged  with  positive  electricity.  On  the  other  hand, 
sealing  wax  receives  a  negative  charge  if  rubbed  witn  flannel.  Positive  elec- 
tricity is  represented  by  a  plus  sign  (+),.  and  negative  electricity  by  the  minus 
sign  (•  -).  Where  the  current  has  treen  perfectly  neutralized  so  that  no  polar- 
ity exist:-,,  a  combination  of  both  signs  is  used  (  +  ). 

While  a  charge  may  be  given  to  a  body  by  contact,  it  is  also  possible 
to  charge  a  body  at  a  distance,  and  by  what  is  known  as  induction.  If 
an  electrified  rod  is  brought  near  a  glass  cylinder,  the  latter  will  receive  a 
temporary  charge  which  disappears  again  when  the  rod  is  removed  from  the 
vicinity  of  the  cylinder.  However,  if 'a  permanent  charge  is  desired,  the  glass 
cylinder  is  touched  by  the  hand  while  the  rod  is  held  in  the  other  hand  near 
the  end  opposite  to  that  being  touched.  A  body  touched  or  grounded  while 
near  a  charged  body  is  electfified  oppositely.  A  body  brought  near  a  charge 
of  electricity  is  electrified  oppositely  on  the  near  end  and  similarly  on  the 
far  end 

The  following  table  represents  electrical  conductors  and  non-conductors 
in  their  respective  value : 

Conductors.  Insulators  (or  non-conductors) 

Silver  Dry  air 

Copper  Shellac 

Other  metals  Paraffin  Ebonite 

Charcoal  Amber  India  Rubber 

Plumbago  Rosin  Silk 

Damp  Earth  Sulphur  Paper 

Water  containing  solids  Glass  Oils 

Moist  air  Mica 

It  must  be  noted  carefully  that  the  conductors  do  not  hold  static  charges 
on  them,  and  are  therefore  known  as  "non-ele.ctrics."  The  insulators,  which 
do  not  carry  current,  hold  static  charges  and  are  known  as  "electrics". 

The  capacity  of  a  body  in  electricity  denotes  its  ability  to  retain  a 
charge.  The  total  quantity  that  can  be  held  depends  directly  on  the  (surface) 
capacity;  but  if  we  consider  a  certain  amount  of  electricity,  it  will" charge  a 
body  of  small  capacity  to  a  higher  degree  than  it  would  one  of  a  larger  capac- 
ity, because  it  can  spread  out  more  on  the  surface  of  the. larger  than  on  the 
smaller. 

One  of  the  most  familiar  types  of  capacity  is  in  the  form  of  a  glass  jar  or 
bottle,  coated  on  its  inside  and  outside  with  tinfoil,  held  on  to  the  glass  by 
shellac  or  other  adhesive.  This  is  known  as  the  Leyden  jar,  Fig.  1,  the  first 


Fig.  1  Fig.  2 

one  having  been  produced  at  Leyden,  Holland.    A  brass  rod  with  a  ball  at  its 
end  is  passed  through  the  wooden  cover  and  makes  contact  either  by  a  chain 


WIRELESS  COURSE— LKSSUN  NO.  1 

or  a  spring  clip  to  the  inner  sides  of  the  tin  foil.  The  outer  foil  may  be  con- 
nected by  other  means.  To  charge  the  Ley  den  jar,  the  outside  coating  is 
grounded  and  the  inside  contact  rod  ball  is  touched  with  some  charged 
body.  To  discharge  the  jar,  the  inner  and  outer  coatings  are  connected 
together  by  means  of  a  discharger,  Fig  2,  which  consists  of  two  connected 
brass  balls  mounted  on  ah  ebonite  handle. 

By  means  of  a  Leyden  jar  having  brass  inner  and  outer  cups  for 
substitutes  to  the  tin  foil,  it  may  be  noticed  that  after  the  jar  has  been  charged 
and  these  carefully  removed,  the  charge  will  not  be  found  in  either  brass 
cup,  proving  that  the  charge  really  is  held  by  the  glass  surface.  It  will  also 
be  noticed  that  in  any  Leyden  jar,  when  it  is  discharged,  there  is  one  large 
spark,  and  an  instant  after  a  weak  spark,  proving  that  the  electric  charge 
soaks  into  .the  glass  dielectric,  and  does  not  release  itself  upon  the  first 
discharge. 

If  a  heavy  charge  of  current  is  to  be  stored,  a  number  of  Leyden  jars  are 
employed,  all  the  inner  coatings  being  connected  together,  and  all  the  outsides 
connected  together  as  shown  in  the  illustration,  Fig.  3.  These  may  all  be 
charged  or  discharged  together. 


The  capacity  of  a  condenser  depends  on  the  size  and  shape  of  the  plate 
and  the  distance  between  them,  as  well  as  the  insulating  medium  (dielectric). 
The  larger  the  plates,  the  greater  the  amount  of  current  required  to  charge 
them,  hence  the  greater  the  capacity.  By  decreasing  the  distance  between 
the  plates  the  capacity  is  also  increased,  since  the  nearer  a  body  is  brought 
under  the  influence  of  a  charged  body,  the  more  electricity  it  will  retain. 

Specific  Inductive  Capacity,  is  the  name  given  to  the  ratio  of  the  capacity 
of  any  condenser,  for  a  given  insulating  material,  to  its  capacity  with  air  as 
a  dielectric.  The  table  below  illustrates  the  relative  dielectric  value  of 
various  materials.  As  an  example  of  -its  use,  if  a  condenser  has  a  certain 
capacity  with  air  as  a  dielectric,  it  will  have  2.05  times  that  capacity  if 
Petroleum  is  substituted  for  the  air  as  the  dielectric. 

Relative  Value  of  Inductive  Capacities. 


Paraffin  1.9 

Carbonic  Acid 1.000 

Air   1. 

Hydrogen 999 

Vacuum  .94 


Glass 6.5    to  10 

Shellac .2.9    to    3.7 

Sulphur    2.8    to    3.2 

Ebonite    2.7 

India  Rubber  2.34 

Petroleum 2.05 

To  produce  static  electricity  in  large  amounts,  a  machine  employing  the 
principle  of  friction  is  often  used  for  experimental  purposes.  There  are 
various  types  of  these  frictional  machines,  the  most  popular  type  being  a 
glass  cylinder  upon  which  a  silk  flap  rubs  as  it  is  turned.  The  charge  is 
gathered  by  appropriate  collectors. 

The  most  successful  machine  of  the  type  illustrated  herewith,  Fig  4  is 
the  influence  static  machine,  which  consists  of  a  number  of  plates  upon  which 
tin  foil  sectors  have  been  placed  These  plates  revolve  in  opposite  directions, 
and  the  current  is  gathered  by  suitable  collectors.  The  small  machine  shown 
in  the  cut  generates  sufficient  current  to  give  a  spark  3  inches  long,  under  all 
conditions,  even  on  a  rainy  day. 


WIRELESS   COURSE-LESSON    NO.  1 


Fig:.  4 
CURRENT  GALVANIC  ELECTRICITY. 

In  the  foregoing  pages  we  have  only  considered  static  electricity,  which 
is  not  used  extensively  in  commercial  activities,  inasmuch  as  it  does  not 
possess  such  useful  characteristics  as  the  current  electricity. 

We  have  three  kinds  of  current  electricity,  as  follows : 

Continuous  or  direct  current,  is  current  which  flows  in  one  direction 
only 

Alternating  current,  is  current  which  vflows  in  opposite  directions  chang- 
ing its  direction  periodically. 

Pulsating  current,  is  current  which  flows  in  one  direction,  but  is  inter- 
rupted periodically. 

In  explaining  the  properties^of  current  electricity  and  the  meaning  of  its 
terms,  a  striking  similarity  between  water  and  the  electric  current  is  made 
use  of  to  serve  as  an  effective  example. 

We  will  therefore  consider  a  tank  of  water  several  feet  above  the  sur- 
rounding ground,  as  in  the  instance  of  reservoirs  of  municipal  water  supplies. 
If  a  pipe  be  connected  to  this  tank,  and  the  pipe  be  brought  to  a  lower  level, 
there  will  be  considerable  pressure  exerted  in  the  water  coming  through  the 
pipe.  This  pressure  may  be  gauged  in  pounds  per  square  inch.  In  elec- 
tricity, we  find  a  current  similar  to  water,  the  pressure  varying  likewise 
according  to  the  source  of  supply.  This  pressure  is  gauged  in  volts,  and  is 
also  referred  to  as  potential.  Volts  therefore  are  the  units  used  to  denote 
the  pressure  of  an  electrical  current.  Coming  back  to  th'e  water  pipe,  we 
note  that  if  the  end  of  the  pipe  is  left  open,  the  water  will  flow  through  .the 
pipe  at  a  certain  rate.  This  may  be  termed  in  gallons  per  minute  if  necessary, 
or  a  smaller  unit,  if  the  rate  of  flow  is  very  slight.  The  rate  of  flow  of  the 
water  will  be  in  proportion  to  the  pressure  of  the  water,  and  also  in  ratio 
with  the  size  of  the  pipe  If  the  pipe  is  larger,  and  the  pressure  greater,  the 
rate  of  flow  is  likewise  higher.  In  electricity,  we  measure  the  flow  of  current 
through  wires  in  the  term  of  Amperes,  and  analogous  to  the  pipe  with  the 
water,  the  greater  the  voltage  (pressure),  and  the  larger  the  conductor,  the 
more  current  will  pass 

For  the  resistance  the  conductors  offer  to  the  electric  current,  as  in  the 
instance  of  the  water  pipe,  the  term  Ohm  is  used.  Ohm  is  the  unit  for 
denoting  the  resistance  offered  to  the  passage  of  electric  current  in  -a  conduc- 
tor. We  therefore  note  that  the  lower  the  number  of  ohms  resistance  in  a 
conductor,  the  greater  the  number  of  amperes  which  will  pass  for  a  given 
voltage.  Also,  the  greater  the  voltage,  the  more  amperes  will  be  passed 
through  a  given  resistance,. 


WIRELESS  COURSE— LESSON  NO.  1 


As  every  part  of  the  conductor  offers  resistance  to  the  flow  of 'electricity, 
a  certain  amount  of  pressure  or  force  is  necessary  to  overcome  this  resistance. 

This  force  is  called  the  ELECTROMOTIVE  FORCE,  or  abbreviated 
E.  M.  F. 

The  unit  in  which  the  E.  JM.  F.  is  measured  is  the  Volt. 

The  E.  M.  F.  is  the  whole  electrical  pressure  existing  in  a  circuit.  This 
force  may  not  be  the  same  at  every  point  in  the  circuit,  and  it  may  vary  in 
pressure  between  one  point  and  another.  This  difference  is  called  the 
POTENTIAL  DIFFERENCE  or  abbreviated  P.  DM  and  is  measured  in 
the  same  unit  as  the  Electro  Motive  Force,  the  Volt. 

In  the  early  part  of  this  lesson,  we  have  learned  that  electricity  of  the 
static  form  can  be  produced  by  friction  and  influence,  but  now  as  we  are 
considering  current  electricity,  we.  will  consider  the  chemical  means  of  pro- 
ducing electric  current. 

If  a  piece  of  copper  sheet,  and  another  piece  of  zinc  sheet  are  placed  in 
a  weak  solution  of  sulphuric  acid  .and  water,  an  electric  current  will  be 
generated,  which  may  be  noted  by  ringing  a  bell.  The  electric  current  is 
formed  through  the  decomposition  of  the  zinc  by  the  powerful  action  of  the 
acid.  The  copper  sheet  is  not  attacked  by  the  acid,  but  is  used  merely  to  form 
the  complete  circuit,  which  starts  from  the  copper  sheet  through  the  con- 
ductor, and  back  to  the  zinc,  after  which  it  goes  through  the  solution  and 
again  reaches  the  starting  point,  the  copper  sheet.  The  two  exposed  plates 
are  named  poles  or  electrodes,  and  sometimes  elements,  Fig.  5.  The  splu- 


CIRCUIT-- 


POSITIVE  PLATE 


ANODE:  OR--- 

+  LLLCTRODL 


+POLL 

fijj*vNEGATIVE  PLATE 


h CATHODE  OR- 
ELECTRODL 


Fig.  6 


tion  is  termed  the  electrolyte,  the  entire  apparatus  being  known  as  a  galvanic 
cell,  or  galvanic  battery.  When  a  number  of  cells  are  combined  together  in 
order  to  obtain  a  heavy  current,  this  group  is  called  a  battery,  though  battery 
is  often  used  incorrectly  to  denote  a  single  cell.  The  flow  of  current  is  always 
from  the  inactive  element  to  the  active,  which  in  the  majority  of  cells  is 
zinc.  The  path  through  which  the  current  is  obliged  to  pass  in  its  journey 
from  one  element  to  the  other  is  termed  the  circuit. 

There  are  many  forms  of  cell,  and  a  description  of  each  type  would 
require  more  space  than  we  can  grant  to  the  subject.  However,  the  most 
used  type  is  the  dry  cell,  see  fig.  6,  which  though  named  a  "dry"  cell,  is  not 
dry,  actually  speaking.  If  such  a  cell  is  opened,  we  find  a  carbon  rod  passing 
through  the  center  and  surrounded  by  absorbent  material,  saturated  with 
the  active  chemical.  The  containing  case  is  made  of  zinc  so  that  the  chemical 
can  attack  it  from  the  inside  and  thus  generate  the  current. 

Another  type  largely  used  in  wireless  telegraphy  by  virtue  of  its  excel- 
lent constant  service  is  the  Catande  Primary  Cell.  The  electrolyte  is  a  solu- 
tion of  caustic  soda,  while  the  plates  are  of  zinc  and  cupric  oxide.  The 
electrolyte  is  usually  covered  with  a  layer  of  paraffin  oil  to  prevent  evapora- 
tion. While  the  cell  furnishes  only  but  .07  volt,  it  has  high  amperage  and 
constancy. 


6  WIRELESS  COURSE— WESSON  NO.  1 

After  a  cell  has  been  used  a  short  interval  of  time  such  as  the  first  cell 
we  described  with  the  copper  and  zinc  plates,  the  voltage  is  noticed  to  decrease 
to  a  point  where  it  cannot  be  used  further.  On  investigating,  it  is  discovered 
that  a  fine  film  of  gas  composed  of  enumerable  bubbles  has  formed  on  the 
copper  plate.  This  is  known  as  the  polarization  of  the  cell.  This  gas  being 
a  non-conductor  of  electricity  for  such  low  potentials  as  are  generated  in 
a  single  cell,  causes  the  voltage  to  be  considerably  reduced.  But,  .fortunately 
there  are  means  of  overcoming  the  formation  of  the  gas,  namely  Depolarizers 
as  for  instance  manganese  oxide.  This  compound  having  a  great  attraction 
for  free  hydrogen,  combines  with  the  hydrogen  surrounding  the  copper  plate 
to  form  other  compounds  which  do  not  interfere  with  the  passage  of  the 
electric  current.  In  dry  cells  the^  manganese  dioxide  is  used,  while  in  the 
Lalande  Primary  Cell  the  copper  oxide  plate  serves  the  purpose.  The  Gerns- 
back  Battery  uses  copper  sulphate  for  depolarizer.  In  some  wet  cells  we  find 
nitric  acid  used,  this  acid  also  possessing  the  characteristic  of  combining  with 
free  hydrogen.  In  the  common  wet  cell  used  in  bell  work  we  find  the  man- 
ganese oxide  mixed  in  with  the  carbon  cylinder  material  as  depolarizer. 

Electric  circuits  are  of  many  varieties.  In  instances  where  the  current 
passes  through  a  number  of  separate  paths  on  its  way  back  to  the  starting 
point,  the  circuit  is  known  as  a  multiple  circuit,  and  the  individual  circuits 
are  said  to  be  connected  in  multiple,  or  parallel.  Fig.  7.  Each  small  branch 


Fig.  1 


CfLLJ  //V  RAf?ALL£L  OR  MULT/PLE. 


"S-*     Fig.  8 


Fig.  9 


CELLS  //V  MULTJPLE  5ER/E5. 


is  known  as  a  shunt  or  branch.  If  all  the  circuits  are  connected  together  i« 
such  fashion  that  the  current  must  travel  through  each  in  perfect  succession, 
then  the  circuit  is  known  as  a  series  circuit.  Fig.  8. 

In  connecting  cells  into  batteries,  it  is  important  to  pay  careful  attention 
to  how  the  cells  are  connected.  If  all  the  cells  are  connected  so  that  the 
zinc  of  one  cell  is  connected  to  the  copper  or  carbon  of  the  next  cell,  they 
will  be  connected  in  series.  The  voltage  in  this  instance  will, .be  equal  to  the 
sum  of  all  the  voltages  of  the  individual  cells,  but  the  amperage  will  be 
equal  to  that  of  one  average  cell.  Qn  the  other  hand,  if  we  connect  all  the 
cells  in  parallel,  connecting  the  zinc  elements  together,  and  the  carbon  or 
copper  elements  together,  then  the  potential  will  be  the  same  as  the  voltage  of 
one  average  individual  cell ;  but  the  current  will  be  equal  to  the  sum  of  all 
the  individual  amperages.  Combinations  can  be  made  so  that  the  desired 
amperage  and  voltage  is  obtained.  Fig.  9. 


WIRELESS   COURSE— LESSON   NO.   1 


THE 

ELECTRO 
STORAGE 
BATTERY 


Fig.  10 

Electricity  may  also  be  stored  as  in  the  instance  of  water.  Such  an 
apparatus  capable  of  storing  electricity  is  known  as  the  storage  battery,  and 
it  operates  on  the  principle  of  causing  certain  chemical  changes  while  current 
is  passing  into  the  cell.  On  the  current  being  disconnected,  these  chemical 
changes  will  begin  a  reverse  action,  generating  an  electric  current,  bee  ngs. 
10,  11. 

Coming  back  to  our  problem  of  water  and  electricity,  we 
water,  the  resistance,  pressure,  and  quantity  of  flow  in  a  pipe,  bear  a  mathe- 
matical relation  to  each  other.  In  electricity,  an  eminent  scientist,  George 
Simon  Ohm,  of  Germany,  (1827)  founded  a  law  showing  the  definite  refc- 
tions  of  resistance,  voltage,  and  amperage,  this  law  being  known  as,  Ohm  s 
Law,  Which  is  the  all  important  factor  in  electrical  calculations. 

Ohm's  Law  states: — 

Electromotive  Force 

Current^ =-. — ;— 

Resistance. 

or  expressed  in  an  Algebraical  equation : 

c=-5 

-R 

Let  us  illustrate  the  application  of  this  rule  in  a  practical^  example.  We 
have  a  winding  which  has  a  resistance  of  100  ohms,  this  having  been  deter- 
mined by  measuring  instruments.  We  want  to  find  the  amount  of  current 
at  25  volts  pressure  which  will  flow  through  this  winding.  Looking  at  Ohm's 
Law,  we  have 

E 


C= 


R 


substituting  the  voltage  (25)  for  the  E,  and  the  ohmage  (100)  for  the  R,  we 
have  the  equation  : 


100  ~ 

c=x 

therefore  the  winding  will  allow  %  ampere  to  pass  through  it.  Ohm's 
Law  may  be  written  in  other  ways,  to  allow  all  factors  included  in  it  to  be 
figured.  Hence  we  have: 

E  for  determining  the  current  consumed  or  passed  by  an 
First:        C=  —  apparatus  or  conductor. 
R 

Second  :     E=CxR  for  determining  the  voltage  required  to  pass  a  definite 
current  through  a  given  resistant 


WIRELESS  COURSE— LESSON  NO.  1 


E  to   determine   resistance   required   for   a   given   current 

Third :       R= and  voltage. 

C 

From  these  three  formulas  most  any  simple  electrical  problem  may  be 
figured.  The  reader  will  undoubtedly  be  able  to  use  these  without  further 
instructions,  and  will  find  these  ^formulas  a  great  help  in  figuring  out  daily 
problems  encountered  in  electrical  work  of  any  kind. 

The  most  important  electrical  units  as  we  have  just  learned  are  the 
ampere,  volt,  and  ohm.  These  units  were  -originally  determined  by 
electrochemical  methods,  in  which  the  decomposition  of  water  was  taken  as 
the  means  of  figuring  the  exact  unit,  but  to-day  both  ammeters  and  voltmeters 
are  used.  These  instruments  consist  of  small  windings  mounted  on  a  metal 
frame-work  which  is  placed  between  the  poles  of  a  permanent  magnet.  As 
the  current  or  voltage  is  increased,  the  needle  which  is  fitted  on  to  the  metal 
frame-work  moves  across  a  scale  and  indicates  the  strength  of  the  voltage  or 
current,  as  the  case  may  be.  The  only  difference'  between  voltmeters  and 
ammeters,  figs.  12,  13,  is  that  they  have  been  marked  differently,  and  that  one 
has  a  suitable  winding  for  the  volts,  while  the  other  is  suited  for  the  amperage. 
Ammeters  are  usually  connected  in  series  with  circuits  in  which  the  amperage 
is  to  be  indicated,  and  voltmeters  are  connected  across  the  two  wires  of  the 
circuit.  In  measuring  resistance,  a  comparison  is  made  between  a  known 
value,  and  the  unknown  resistance  in  the  circuit  being  tried.  An  instrument 
indicates  when  both  circuits  are.  evenly  balanced,  and  then  by  reading  the 
amount  of  resistance  in  the  known  circuit^  the  ohmage  of  the  unknown  circuit 
is  determined.  This  apparatus  is  known  as  the  Wheatstone  Bridge. 


Fig.  12 


Fig.  13 


.  Other  terms  have  been  derived  from  the  three  units  we  have  discusssed 
in'  the  preceding  paragraphs.  Watt  is  a  term  which  combines  volts  and 
amperes;  one  watt  being  equal  to  a  current  of  one  ampere  at  a  pressure  of 
one  volt.  If  we  have  a  current  of  10  amperes  and  50  volts  potential,  we  have 
500  watts.  If  we  have  a  pressure  of  2  volts,  and  a  current  of  3  amperes,  we 
have  a  wattage  of  6.  All  statements  of  current  made  in  watts  are  more 
definite  then  merely  in  either  volts  or  amperes,  since  individually  these  units 
are  not  complete  without  the  other.  If  we  have  a  current  of  one  watt  for  one 
hour,  it  is  known  as  a  watt-hour.  If  we  have  a  current  of  1,000  watts,  it  is 
called  a  kilowatt,  this  unit  being  the  standard  for  the  calculation  of  heavy 
currents.  Transformers  for  wireless  telegraphy  are  rated  in  kilowatts,  as 
well  as  dynamos.  Electric  current  is  sold  by  the  kilowatt-hour,  which  means 
the  using  of  1,000  watts  for  one  continuous  hour.  It  requires  746  watts  to 
equal  one  mechanical  horse-power  when  comparing  mechanical  and  electrical 
energy.  Thus  it  will  be  noted  that  a  one  kilowatt  motor  is  about  1%  H.  P. 
One  mechanical  horse-power  is  the  force  required  to  raise  33,000  Ibs.  one  foot 
high  in  one  minute. 


WIRELESS  COURSE 


THE  PRINCIPLES  OF  MAGNETISM. 

E  name  "Magnet"  originated  from  the  name  of  a  town,  Magnesia,  in  Asia  Minor, 
where  the  loadstones,  which  could   attract   small   particles   of  iron,  were   first 
found.    The  first  discovery  is  recorded  as  having  been  made  by  the  philosopher 
Plato,  who  was  borne  480  years  before  the  dawn  of  the  Christian  Era. 

Magnetism  is  found  in  nature  in  the  form  of  ore,  commonly  known  as  loadstone, 
or  magnetite  by  the  minerologists.  It  is  found  in  many  parts  of  the  world,  and  in 
the  United  States  there  is  a  fair  supply.  The  compass,  fig.  1,  a  magnetic  device,  is  an 
invention  which  rendered  navigation  over  seas  possible,  and  is  attributed  to  the 
Chinese  whom  are  said  to  have  used  it  before  it  became  known  in  Europe. 

After  400  years  following  the  invention  of  the  compass,  Dr.  Gilbert,  who  will 
be-  recalled  by  the^r.eader  as  the  first  active  worker  in  static  electricity,  published  in 
England  his  famous  work  "De  Magnete"  in  the  year  1600,  which  comprised  a  complete 
account  of  the  remarkable  characteristics  of  magnetism. 


Fig.  1. 


Fig.,  la 


If  a  bar  of  iron  is  taken  and  treated  with  a  loadstone,  it  will  become  possessed  of 
magnetism.  If  suspended  on  a  thread.,  fig.  la,  it  will  point  north  and  south,  acting  as  a 
compass.  The  end  pointing  north  is  the  south  pole  of  the  compass,  while -the  end 
pointing  south  is  the  north  polf.  If  a  needle  or  other  steel  object  be  brbught  near  the 
bar  magnet,  it  will  be  attracted  at  either  end,  but  in  the  center  of  the  bar  there  will 
be  found  comparatively  no  magnetism.  This  illustrates  that  the  magnetism  at  the 
center  is  neutral,  increasing  in  strength  toward  the  ends  and  in  opposite  polarity  of 
magnetism  at  these  ends. 

Now,  if  the  bar  magnet  be  laid  under  a  piece  of  white  paper  and  coarse  iron  filings 
be  scattered  over  the  paper,  the  filings  will  arrange  themselves  in  wave-like  formation, 
the  lines  extending  horn  the  magnetic  poles,  and  in  faint  lines  circling  to  the  opposite 
poles,  fig.  2.  These  lines  represent  the  magnetic  lines  of  force,  which  extend  from 


Fig.  2 

one  pole  to  the  other  in  all  magnets,  the  strength  being  less  as  the  distance  from  the 
poles  increases.  These  lines  of  force  in  passing  from  one  pole  to  the  other  are  known 
as  the  magnetic  circuit,  fig.  3.  A  closed  magnetic  circuit  is  one  where  the  magnetism  is 
limited  to  a  continuous  iron  mass,  the  magnetism  having  no  gaps  to  cross  in. order  to 
complete  its  magnetic  circuit  from  one  pole  to  the  other.  A  closed  magnetic  circuit  is 
usually  employed  in  watchcase  telephone  receivers  and  possesses  many  advantages 
over  the  open  magnetic  type.  The  open  magnetic  circuit  is  one  in  which  there  are  air 
gaps  for  the  lines  of  force  to  bridge  in  th'eir  travel  from  one  pole  to  the  other.  This 
form  of  magnetic  circuit  is  the  one  largely  employed. 

We  have  learned  that  a  magnet  always  possesses  two  poles,  the  north  and  the 
South,  represented  by  N  and  S  respectively". 

Copyright  1912  by  B.  I.  Co. 


10 


WIRELESS  COURSE— LESSON  NO  2 


HORSE-SHOE  MAGNET 


I 

lit 


BAR   MAGNET 


*\ 


V 


Fig.  3  "~~    • — •""* 

If  we  consider  the  earth  as  the  fundamental  magnet,  then  in  comparison  with  it, 
we  ought  to  call  that  pole  of  any  magnet  which  tends  to  point  north,  a  south  pole,  and 
vice  versa.  The  so-called  north  pole  or  end  of  a  compass  needle,  is  thus  really  a  south 
pole,  and  its  south  pole  or  end,  is  a  north  pole.  The  reason  for  this  inaccuracy  is 
probably  due  to  the  mariner's  compass  being  the  first  general  .practical  application 
of  magnetism.  That  end  of  the  needle  which  points  always  to  the  north  would 
naturally  be  called  its  north  end.  According  to  the  modern  theory  of  magnetism 
this  is  an  inaccurate  name  for  it.  A  more  correct  designation  would  be  the  north- 
seeking  end  or  pole. 

If  we  take  a  magnet  and  suspend  it  on  a  thread,  it  will  point  north  and  south, 
so  that  we  can  mark  the  ends  with  the  polarity  they  possess.  The  end  pointing  north 
being  marked  with  an  "S"  and  the  end  pointing  south  with  an  "N."  If  we  treat 
another  bar  magnet  in  the  same  manner,  we  can  then  bring  the  last  magnet  near  to  the 
suspended  magnet  so  that  both  "S"  poles  are  near  together.  The  suspended  magnet 
will  immediately  begin  to  turn  away  from  the  other  magnet,  showing  that  there  is  a 
repulsion.  Now,  if  the  "N"  poles  are  treated  in  the  same  way  the  results  will  be  the 
same,  which  teaches  us  that  like  poles  in  magnetism  repel  each- other,  identically  as  in 
static  electricity.  Then  if  the  "S"  pole  of  one  magnet  is  brought  near  to  the  "N"  pole 
of  the  other  magnet,  there  will  be  an  attraction;  the  suspended  magnet  turning  and 
following  the  one  held  by  the  hand.  Unlike  poles  attract  each  other.  It  will  be 
noticed  that  if  it  were  possible  to  reverse  the  polarity  of  the  magnets  at  a  critical 
moment,  so  that  opposite  poles  would  attract  each  other  while  the  like  poles  would 
repel  each  other,  the  suspended  magnet  would  assume  a  rapid  rotary  motion,  depend- 
ing on  the  frequency  in  the  reversal  of  polarity.  This  is  the  principle  of  the  electric 
motor,  the  magnetism  being  changed  at  the  critical  moment  by  means  of  electricity. 
Magnetic  bodies  are  those  which  can  acquire  and  retain  magnetism. 
Paramagnetic  bodies  are  those  which  are  attracted  by  magnetism. 
Diamagnetic  bodies  are  those  which  are  repelled  or  on  which  magnetism  has  no 
effect.  The  following  table  illustrates  common  metals  and  substances  in  their  relative 
magnetic  order. 

Paramagnetic.  Diamagnetic. 

Iron  Bismuth 

Nickel  Phosphorus 

Cobalt  Antimony 

Manganese  Zinc 

Chromium  Mercury 

Cerium  Lead 

Titanium  Silver 

Palladium  Copper 

Platinum  Gold 

Oxygen  Water 

Ozone  Alcohol 

Tellurium 
Selenium 
Sulphur 
Thallium 


Fig.  4 

Fig.  5  (Courtesy  "Modern  Electrics.") 

The  best  method  of  forming  a  bar  magnet  is  to  magetize  each  end  individually. 

One  end  is  first  rubbed  from  the  center  to  the  end  by  a  permanent  bar  magnet  and  then 


WIRELESS  COURSE— LESSON  NO  2  11 

the -opposite  end  is  rubbed  from  the  center  to  the.  other  end,  as  shown,  in  the  sketch, 
fig.  4  with  the  opposite  pole. 

A  horse-shoe  type  of  magnet  as  generally  sold  by  electrical  houses,  see  fig.  5,  is 
nothing  more  than  a  bar  magnet  with  its  two  ends  brought -near  to  each  other  by 
bending  it.  While  not.  in  use,  a  small  piece  of  steel  is  placed  across  both  poles,  this 
piece  being  known  as  the  "keeper."  Its  purpose  is  to  form  a  closed  magnetic  circuit 
and  thus  help  to  retain  the  magnetism. 

If  a  magnet  be  placed  in  acid  so  that  the  outside  surface  be  attacked  and  dissolved, 
it  will  be  found  that  the  magnetism  is  greatly  lessened,  if  not  entirely  destroyed.  This 
proves  that  the  magnetism  is  largely  confined  to  the  surface.  For  this  reason,  it  is 
advisable  to  use  a  greater  number  of  smaller  magnets,  in  order  that  a  large  surface 
may  be  thus  formed.  In  practice  this  method  is  employed,  a  number  of  permanent 
magnets  with  all  the  "N"  poles  together  and  all  the  "S"  poles  together,  and  havirig 
one  common  iron  pole  for  each  polarity  is  used,  the  magnets  so  made  being  known 
as  laminated,  built-up,  or  compound  magnets. 

Heat  has  a  temporary  effect  of  removing  magnetism  from  bodies,  but  only  while 
the  body  is  heated,  the  magnetism  again  being  present  when  the  metal  cools.  Jarring 
a  magnet  will  permanently  weaken  it,  the  degree  of  loss  being  in  proportion  to  the 
conditions.  Inasmuch  as  many  conditions  effect  permanent  magnets,  in  the  electrical 
industry  where  magnets  are  manufactured  for  accurate  purposes,  as  in  measuring 
instruments,  the  process  is  thorough,  and  the  magnets  subjected  to  boiling,  jarring, 
and  other  tests  so  that  the  surplus  magnetism  may  be  removed  and  absolute  per- 
manency assured. 

A  magnetic  circuit  is  similar  to  an  electric  circuit,  starting  from  one  pole  and 
travelling  to  the  other  pole.  Magnetism  may  be  produced  inductively,  by  bringing 
a  permanent  magnet  in  the  vicinity  of  a  piece  of  iron  or  steel,  when  this  object  will 
be  found  to  possess  magnetism,  but  it  loses  this  -power  as  soon  as  the  permanent 
magnet  is  removed  to  a  greater  distance  where  the  magnetic  lines  of  force  become 
too  weak  to  induce  magnetism.  It  is  also  possible  to  locate  magnetism  in  a  piece  of 
steel  rod,  so  that  the  various  sections  will  ha.ve  north  and  south  poles.  This  is 
accomplished  by  magnetizing  the  independet  sections  with  a  powerful  magnet.  It 
is  also  possible  for  steel  or  iron  to  carry  magnetism  through  it  yet  only  be  magnetized 
as  long  as  in  actual  contact  with  the  permanent  magnet  exists.  The  best  grades  of 
steel  retain  the  magnetism  the  longest  time,  and  display  great  permanency.  The  softer 
the  steel,  the  less  efficient  it  is  for  use  as  a  permanent  magnet.  Iron  is  less  efficient; 
the  softer  grades  being  worthless  for  making  permanent  magnets.  For  this  reason, 
soft  iron  is  used  in  electro-magnets  where  it  must  be  completely  demagnetized  after 
the  passage  of  the  electric  current. 

ELECTRO-MAGNETISM. 

Early  experimenters  suspected  that  some  relation  existed  between  magnetism 
and  electricity,  but  it  was  not  until  1819  that  this  was  proven  by  Oersted  of  Copen- 
hagen, Denmark.  He  demonstrated  that  a  wire  carrying  a  current  would  deflect  a 
compass  needle.  The  needle  tends  to  turn  at  right  angles  to  the  direction  of  the 
current  in  the  conductor,  the  degree  of  the  angle  being  in  proportion  to  the  strength 
of  the  current.  The  illustration,  fig.  6,  represents  the  direction  of  'the  current  and 
the  position  of  the  N  and  S  poles  of  the  needle. 


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Fig.  6  Fig.  7 

Around  a  wire  carrying  an  electrical  current,  a  magnetic  field  is  formed.this 
field  extending  in  concentric  lines  further  and  further  away  from  the  conductor, 
Only  current  electricity  produces  marked  magnetic  effects  in  conductors,  static  elec- 
tricity having  no  appreciable  effect. 

In  the  next  cut,  fig.  7,  are  represented  the  lines  of  force  in  dotted  lines  produced 
by  two  opposite  flowing  currents  in  two  wires. 

If  we  take  a  heavy  piece  of  wire  and  bend  it  so  as  to  pass  over  and  under  a 
pivoted  compass  needle  as  shown  in  the  cut,  fig.  8,  it  will  be  found  that  by  connecting: 
both  binding  posts  to  a  source  of  current,  this  current  may  be  detected  by  the 
reflection  of  the  compass  needle  as  well  as  its  relative  strength.  This  instrument  is 
known  as  the  galvanometer,  and  in  its  more  complicated  and  perfected  forms  is 
used  for  detecting  feeble  electric  currents. 


12 


WIRELESS  COURSE— LESSON  NO  2 


If  a  wire  carrying  an  electric  current  is  wound  into  a  spiral  form,  it  will  exert  a 
powerful  magnetic  field  in  the  direction  of  its  axis,  the  polarity  being  controlled  by 
the  flow  of  current '"as  illustrated  by  the  accompanying  cut, -fig.  9.  This  wire  coil  is 
called  a  solenoid. 


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s  :5£££fim 


Fig,  8 
(Courtesy  "Modern  Electrics.") 


^  ^x 

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Fig.  9 


If  a  number  of  turns  of  wire  be  wound  on  a  wooden  spool  and  current  passed 
through  the  winding,  a  small  iron  rod  will  be  pulled  into  the  spool.  If  a  spring 
balance  is  connected  to  the  rod,  the  strength  of  the  pull  may  be  gauged.  A  form  of 
commercial  meter  formerly  used  and  known  as  the  "plunger"  voltmeter  employed 
this  principle,  the  spring  being  in  this  case  fitted  with  a  pointer  which  indicated  on 
a  scale  marked  in  volts,  and  if  desired  the  scale  could  be  graduated,  in  amperes 
instead.  If  iron  is  used,  it  will  be  pulled  into  the  spool,  no  matter  in  what  direction 
the  current  is  flowing,  inasmuch  as  soft  iron  does  not  possess  permanent  magnetism 
and  is  therefore  attracted  by  magnetism  of  either  polarity. 

To  construct  an  electromagnet,  a  piece  of  soft  iron  is  first  covered  with  a  thin 
sheet  of  paper,  in  order  that  the  curretit  flowing  through  the  wire  will  not  form  a 
by-path  through  the  iron  accidently,  this  being  called  "grounding."  Over  the  paper, 
the  layers  of  wire  are  wound,  there  being  two  end  pieces  (coil  or  spool  heads)  in  order 
to  secure  the  winding  in  place,  these  being  either  of  fibre  or  hard  rubber.  The  iron 
rod  around  which  the  winding  is  placed  is  known  as  the  core.  The  accompanying 
diagram,  fig,  10,  represents  the  polarity  imparted  in  the  core  with  the  direction  of 
current  given.  In  order  to  obtain  the  maximum  efficiency  from  electromagnets,  usually 
two  are  mounted  on  one  steel  or  iron  bar,  the  N  .and  S  poles  being  connected 
together.  This  greatly  increases  the  magnetic  force  for  a  given  current  strength, 
the  gain  being  derived  through  the  reduction  of  the  magnetic  leakage.  The  electro- 
magnet when  subjected  to  alternating  magnetizing'  currents,  produces  a  heating  effect 
in  the  iron  core  which  is  known  as'  hysteresis. 


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POLAKfTY  Of  £L£CT#0  AfJG/VcTS 


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OBL/QUELY  CROSSED  CONDUCTORS 


Fig.   10 


Fig.  11 


Hysteresis  is  that  magnetic  inertia  or  resistance  to  change  in  polarity  of  the 
molecules  evidenced  whenever  the  magnetizing  power  is  reversed  or  changed  The 
molecules  of  the  iron  resist  this  change  in  polarity,  and  this  results  in  molecular 
friction,  (as  it  is  often  called),  whenever  the  reversal  of  magnetism  is  raised  to 
a  certain  frequency  or  number  of  times  per  second,  the  hysteresis  effect  or  frictidn 
is  soon  made  evident  by  the  heating  of  the  iron  mass. 

This  phenomenon  of  electromagnetic  induction  will  be  treated  upon  again  in  a  later 
chapter,  dealing  with  detectors. 

ELECTRODYNAMICS. 

Electrodynamics  is  that  branch  of  electrical  study  which  deals  with  the  action  of 
one  current  carrying  conductor  upon  another  one. 

One  of  the  laws  relative  to  electrodynamics  is: 

Two  parallel  conductors  attract  each  other  when  the  currents  therein  flow  in  the 
same  direction,  and  repel  each  other  when  the  currents  flow  in  opposite  directions. 

This  rule  is  applicable  whether  the  wires  are  of  the  same  or  different  circuits, 
and  whether  the  wires  are  straight  or  curved. 

Another  rule  applying  to  the  action  of  conductors  states: 

Conductors   crossing  each   other  obliquely  tend  to   take  up   a   position   in  which 


WIRELESS  COURSE— LESSON  NO  2 


13 


they   Are  parallel  and  the   currents   in   them  are  flowing  in  opposite  directions.     This 
is  illustrated  in  the  accompanying  fig.  11. 

There  is  no  tendency  for  the  wires'  to  be  attracted  or  repulsed  lengthwise,  the 
action  being  entirely  sideways.  For  illustrating  the  attraction  and  repulsion  of 
electrical  conductors,  an  apparatus  known  as  "Ampere's  Stand"  is  employed.  In 
the  cut,  fig.  12,  the  principle  is  briefly  shown,  the  instrument  consisting  of  two  heavy 
loops  of  wire,  one  being  pivoted  so  as  to  freely  revolve,  while  the  other  .is  fixed. 
Currents  from  different  circuits  'may  be  used  on  both  coils. 


Fig.  12 


Fig.  13 


ELECTROMAGNETIC  INDUCTION. 

Electromagnetic  induction  is  the  production  of  electric  current  in  a  wire,  through 
the  action  of  a  magnetic  field. 

In  1831,  Faraday  of  England,  demonstrated  that  the  motion  of  a  magnet  near  a 
closed  circuit  produced  an  electric  current  in  that  circuit.  Moving  the  circuit  and 
keeping  the  magnet  still  produces  the  same  result,  the  essential  element  being  to  cut  the 
magnetic  lines  of  force  by  the  moving  of  the  wire  or  magnet.  An  apparatus 
producing  this  effect  consists  of  a  bobbin  of  wire  connected  to  a  galvanometer.  When 
a  permanent  bar  magnet  is  plunged  into  the  center  of  the  spool,  there  is  a  deflection 
of  the  needle,  proving  that  a  current  has  been  produced.  But,  as  soon  as  the  bar  comes 
to  rest  against,  the  bottom  of  the  spool  there  is  no  further  deflection  of  the  galvano- 
meter needle,  and  it  returns  to  its  normal  position.  However,  as  soon  as  the  bar  is 
pulled  out  of  the  spool,  the  galvanometer  needle  swings  in  the  opposite  direction 
demonstrating  that  a  current  has  been  produced,  which  flows  in  the  opposite  direction 
to  that  produced  when  the  bar  was  being  plunged  into  the  spool.  It  is  therefore 
noted  that  the  .current  induced  in  the  circuit  is  governed  by  the  movement  of  the 
magnet.  While  either  the  spool  or  magnet  remains  stationary  there  is  no  current 
produced,  but  upon  altering  the  position  of  either  factor,  a  current  is  generated. 

If  in  place  of  a  bar  magnet  we  substitute  a  small  coil  of  wire  which  can  fit  into 
the  larger  spool,  and  in,  which  current  has  been  turned  on,  we  find  that  upon  plunging 
this  spool  into  the  larger  spool,  a  current  is  again  produced.  As  soon  as  this  spool 
is  removed,  a  current  in  the  opposite  direction  is  induced,  exactly  as  in  the  instance 
of  the  bar  magnet,  fig.  13. 

In  the  two  preceding- methods,  the  position  of  the  two  elements  has  been  altered 
in  order,  to  create  the  induced  current.  Now,  if  we  place  the  smaller  coil  within  the 
larger  one  and  break  the  electric  current  in  the  exciting  spool,  a  current  will  be 
detected  in  the  other  circuit.  When  the  current  is  turned  on  in  the  exciting  circuit, 
the  galvanometer  again  detects  a  current,  but  in  the  opposite  direction.  Thus  by 
making  and  breaking  the  circuit  of  the  smaller  coil,  it  is  possible  to  induce  a  periodic 
current  in  the  other  circuit.  The  smaller  coil  may  be  termed  the  primary,  inasmuch  as 
it  contains  the  current  which  produces  the  magnetic  flux,  and  the  other  coil  which 
receives  the  induced  current  may  be  termed  the  secondary.  It  is  by  applying  this 
principle  that  the  induction  coils  and  transformers  for  wireless  telegraphy  render  it 
possible  to  raise  a  low  potential  to  a  high  potential,  in  virtue  of  the  ratio  existing 
between  the  number  of  terms  in  the  two  coils. 

The  lines  of  force  of  a  magnetic  field  ar,e  termed  "magnetic  flux,"  and  measured 
by  the  mmber  of  the  lines  per  unit  area  of  the  field.  Whenever  the  amount  of  flux 


14 


WIRELESS  COURSE— LESSON  NO  2 


that  passes  within  a  closed  electrical  circuit  is  changed  for  any  cause,  there  is  set  up 
an  induced  current  in  this  circuit.  The  circuit  must  always  cut  the  lines  of  force  at 
right  angles,  for  the  maximum  effect  is  then  obtained.  There  is  no  current  induced 
if  the  circuit  moves  in  parrallel  direction  to  that  of  the  lines  of  force. 

The  principle  of  electro-magnetic  induction  as  applied  to  telephones  and  telephone 
receivers  is  shown  by  fig.   14,  the  permanent  bar  magnets   having  two  coils   of  wire 


Fig.  14 

placed  at  their  ends  and  any  change  in  the  current  strength  traversing  them,  results 
in  a  change  of  the  magnetic  flux,  attracting  the  iron  diaphragm.  The  current  in  this 
case  is  set  up  and  varied  by  the  voice  air  currents  inpinging  upon  one  diaphragm, 
thereby  causing  a  change  in  the  lines  of  force,  and  results  in  the  production  of  the 
current. 

The  direction  of  the  induced  current  will  be  opposite  to  that  in  the  exciting 
circuit  when  the  current,  is  turned  on.  If  the  current  is  turned  off,  the  current  in 
both  circuits  will  be  in  the  same  direction. 

If  a  disc  of  copper  or  other  metal  is  moved  in  a  magnetic- field,  there  will  be 
induced  currents  in  the  metal  mass,  these  currents  being  known  as  Eddy  currents. 
If  the  rotation  of  the  disc  is  continued  for  a  certain  length  of  time,  the  disc  will 
become  heated  through  the  action  of  these  Eddy  currents.  These  currents  flow  in 
round  circles,  and  oppose  the  rotation  of  the  mass  through  the  magnetic  field.  If  the 
disc  be  rapidly  spun  and  the  driving  power  removed,  it  will  come  to  an  abrupt  stop 
owing  to  the  drag  exsisting  between  the  Eddy  currents  and  the  magnetic  field.  For 
this  reason,  metal  discs  or  masses  are  employed  extensively  in  electrical  instruments 
where  it  is  desired  to  secure  a  damping  effect,  as  well  as  in  electric  brakes  which  have 
been  used  for  street  cars  with  some  success.  In  motors  and  dynamos,  the  rotating 
portion  known  as  the  armature  is  laminated,  the  entire  mass  consisting  of  a  great 
number  of  thin  iron  punchings  which  have  been  individually  coated  with  insulating 


WIRELESS  COURSE— LESSON  NO  2 


15 


paint.  Thus  each  punching  is  insulated  from  its  neighbor,  and  the  Eddy  currents  thus 
reduced  to  a  minimum. 

When  a  wire  is  moved  through  a  magnetic  field,  a  mechanical  drag  is  encountered, 
due  to  the  opposition  of  the  current  generated  in  the  wire.  If  the  ends  of  the  wire 
be  connected  the  mechanical  resistance  becomes  more  pronounced.  In  all  instances 
of  electromagnetic  induction,  the  induced  currents  have  such  a  direction  that  their 
reaction  tends  to  stop  the  motion  producing  them. 

From  the  foregoing  it  has  been  learned  that  circuits  have  inductive  effects  upon 
each  other,  but  these  circuits -also  have  inductive  effects  upon  themselves,  .this  being 
termed  self-induction  or  inductance. 

The  unit  of  inductance  is  the  Henry,  and  inductance  is  represented  by  the 
symbol-letter  L.  The  effect  of  inductance  is  not  as  noticeable  in  short  lengths  of 
wire  as  in  long  lengths,  and  the  action  is  considerably  augmented  by  winding  the 
wire  in  coils.  If  an  iron  rod  is  introduced  in  the  center  of  the  coil,  the  effects  will  be 
greatly  increased.  By  constructing  a  small  coil  with  an  iron  core  and  connecting  it 
to  a  powerful  battery,  it  will  be  noticed  that  upon  opening  the  circuit  a  heavy  spark 
is  caused  at  the  break.  If  the  terminals  of  the  battery  alone  be  connected  for  an 
instant  and  disconnected,  the  spark  will  be  entirely  different  and  much  smaller  than 
the  spark  caused  when  the  circuit  with  the  coil  is  broken.  This  illustrates  that  there 
is  an  extra  current  produced  by  the  action  of  the  coil  upon  the  circuit.  If  the  hands 
be  placed  across  the  two  wires  which  are  disconnected  to  open  the  current,  a  shock 
will  be  experienced.  If  the  hands  are  placed  across  the  battery,  no  shock  will  be 
felt.  This  proves  that  the  current  produced  by  self-induction  is  of  a  higher  voltage 
than  that  of  the  battery  supplying  the  current  to  the  coil.  This  principle  of  self- 
induction  is  used  in  gas-lighting  coils,  where  many  turns  of  wire  are  wound  upon  an 
iron  core.  These  coils  give  a  heavy  spark  upon  the  opening  of  the  circuit.  Primary 
coils  for  ignition  of  gas  and  gasoline  engines  are  made  in  the  same  manner. 

INDUCTION  COILS  AND  TRANSFORMERS. 

It  has  been  learned  that  if  a  small  coil  of  wire  is  placed  within  a  larger  coil^and 
interrupted  current  passed  thrcmgh  the  smaller  coil,  there  will  be  a  current  induced  in 
the  larger  coil.  If  an  iron  core  is  placed  within  the  smaller  coil,  the  action  will  be 
more  pronounced.  Based  upon  these  facts,  an  apparatus  known  as  the  Induction  coil, 
also  called  Spark  coil,  for  the  conversion  of  low  voltage  currents  to  high  voltage 
currents  has  been  produced.  The  induction  coil,  Fig.  15,  consists  essentially  of  a  core, 
usually  made  of  straight  lengths  of  soft  iron  wire,  in  order  that  the  magnetism  be 


L 

M 

A  J 

M  1 

/T      <±-B 

I/  I/  I 

PJL 

l/vf  \^\/ 

COIL 

,///  ,j/  1  L 
\T  V  f 

IT  ^j 

c 

F==i 

Fig.  15 


Diagram  of  Induction  Coil. 


only  present  when  the  current  is  passing  through  the  surrounding  winding.  Over 
«:his  iron  core,  insulating  tape  is  carefully  wound,  in  order  to  insulate  the  currents 
from  the  core,  and  on  the  tape  a  number  of  layers  of  heavy  wire  are  placed.  This 
is  termed  the  primary  winding,  the  core  and  the  winding  mentioned  together  form  the 
primary.  Over  the  primary  is  placed  a  hard  rubber  or  fibre  tube  as  a  precaution 
against  the  sparking  of  the  secondary  into  the  primary.  Surrounding  this  tube  are 
the  many  turns  of  fine  copper  wire  known  as  the  secondary  winding.  In  order  to 
facilitate  the  construction  and  future  repairing  of  these  secondaries,  the  windings 
are  placed  on  small  spools  or  sections,  which  also  increases  the  insulating  value. 


K)  WIRELESS  COURSE— LESSON  NO  2 

These  sections  are  known  as  "pies."  The  entire  secondary  winding  when  completed 
is  subjected  to  a  thorough  soaking  in  an  insulating  compound  which  has  been  heated 
to  a  liquid  state.  As  it  cools,  it  forms  a  solid  mass  of  the  winding  which  is  thus 
thoroughly  insulated.  The  end  wires  lead  to  a  pair  of  binding,  posts  usually  .located 
at  the  top  of  the  Cjoil,  and  to  these  binding  posts  may  be  connected  a  pair  of  spark 
balls  with  the  rods  and  insulated  handles.  On  one  end  of  the  induction  coil  is  a  spring 
carrying  a  heavy  iron  disc  at  its  uppermost  portion.  The  spring  is  fitted  with  a 
platinum  point  which  strikes  against  a  similar  point  located  at  the  end  of  a  brass 
adjustment  screw.  This  is  known  as  the  vibrator  or  interrupter,  the  screw  being 
known  as  the  adjustable  contact  screw.  The  interrupter  serves  the  purpose  of 
automatically  making  and  breaking  the  primary  current  with  which  it  is  connected 
in  series.  The  magnetism  of  the  core  attracts  the  iron  disc  which  is  drawn  to  it.  In 
so  doing  it  moves  the  spring  which  separates  the  contact  points  and  thus  opens  the 
circuit.  The  current  being  disconnected,  leaves  the  core  without  magnetism  which 
allows  the  disc  to  return  to  its  former  position  and  again  make  contact  with  the 
adjustment  screw,  and  thus  begin  the  action  over  again.  A  large  condenser  made  of 
paraffined  paper  and  tin  foil  is  bridged  across  the  interrupter  contacts  to  reduce  the 
sparking  caused  by  the  self-induction  of  the  primary,  this  condenser  being  known  as 
the  primary  condenser. 

A  transformer  is  an  apparatus  consisting  of  two  windings  placed  on  the  same 
core  for  the  purpose  of  transfering  the  current  from  the  one  coil  to  the  otHer  by 
means  of  electromagnetic  induction.  There  are  two  main  divisions  of  transformers, 
the  open  core  and  the  closed  core.  The  open  core  is  one  in  which  the  iron  magnetic 
circuit  is  open,  the  core  consisting  of  but  a  single  straight  rod  with  both  ends  point- 
ing in  opposite  directions.  The  closed  core  transformers  is  one  in  which  the  iron 


®  CLOSED  AMD  OPEM  CORE 

Fig.  16 

magnetic  circuit  is  continuous,  the  core  being  continuously  joined.  Fig.  16.  The  most 
common  form  of  closed  core  transformer  is  that  in  which  the  core  consists  of  four 
square  cores  joined  together  to  form  a  perfect  rectangle.  Closed  core  transformers 
are  preferred  to  open  core  types  for  the  reason  that  the  percentage  of  loss  is  much 
less  than  in  the  open  core  type,  due  to  the  more  efficient  magnetic  circuit  which  has 
the'  minimum  loss  of  flux.  In  the  open  core,  there  is  a  certain  loss  of  magnetic  flux 
at  both  ends.  Transformers  may  be  operated  by  alternating  current,  and  are  rated  in 
kilowatts.  Open  core  transformers  may  also  be  used  on  direct  currents,  as  in  the 
instance  of  the  induction  coil,  but  a  means  of  interrupting  the  current  must  be  pro- 
vided. A  small  electric  motor  carrying  a  contact  which  makes  and  breaks  the.  circuit 
may  be  employed.  For  all  open  core  transformers  and  induction  coils,  a  type  known 
as  the  electrolytic  interrupter  may  be  used,  which  is  described  in  a  future  lesson,  but 
it  cannot  be  used  on  closed  core  transformers. 


WIRELESS  COURSE— LESSON  NO.  3 


17 


Lesson  Number  Three. 

DYNAMOS,   MOTORS,    GENERATORS    AND   WIRING. 

N  studying  the  principles  of  magnetism  the  student  will  remember  that  the 
attracton  and  repulsion  was  caused  by  the  action  of  like  and  unlike  magnetic 
polarities.  This  principle  has  been  applied  in  the  electric  dynamo,  which  is  in 
reality  an  electro-magnetic  engine,  since  the  electricity  must  be  converted  into  mag- 
netism before  the  dynamo  can  operate. 

As  we  have  seen  in  a  previous  lesson,  it  was  Faraday,  who  in  1831  discovered 
this  principle.  The  electromagnetic  engines  are  the  following: 

The  Dynamo.  The  dynamo  is  a  machine  converting  mechanical  energy  into 
electrical  energy,  or  electrical  energy  into  mechanical  energy. 

The  Generator.  If  the  dynamo  is  used  to  transform  mechanical  energy  into 
electrical  energy,  it  is  called  a  generator. 

The  Motor.  If  the  dynamo  is  used  to  transform  electrical  energy  into  mechanical 
energy  it  is  called  a  motor. 

An  Alternator  is  a  machine  converting  mechanical  energy  into  electrical  alter- 
nating current. 


Fig.  1.  Fig.  2 

In  the  accompanying  illustration,  fig.  1,  will  be  noticed  the  parts  of  a  small  battery 
motor,  while  the  complete  assembled  motor  is  seen  in  fig.  2.  The  armature  is  the 
rotating  member  of  the  motor,  and  in  this  instance  contains  three  iron  pole  pieces 
upon  which  are  placed  the  windings.  These  windings  are  connected  to  three  brass 
or  copper  segments  shown  to  the  left  of  the  armature  and  mounted  on  the  same 
shaft  which  also  holds  the  pulley.  These  segments  are  known  as  the  commutator, 
and  its  purpose  is  that  of  changing  the  polarity  of  the  magnetism  in  the  three  pole- 
pieces  of  the  armature  at  the  critical  instant,  so  that  like  and  unlike  poles  will  be 
approaching  each  other  at  the  correct  moment  so  as  to  impart  a  rotary  motion  to  the 
armature.  On  this  commutator,  two  copper  strips  press  at  opposite  sides,  and  are 
known  as  brushes,  being  held  in  suitable  clamps  which  are  termed  brush-holders. 
These  brushes  convey  the  current  to  the  rotating  commutator.  The  field  contains  a 
winding  and  thus  produces  a  powerful  magnetic  flux  in  the  space  in  which  the  armature 
i  evolves. 

Larger  motors  employ  the  same  principles  and  similar  parts,  though  naturally 
these  must  be  of  larger  construction  and  improved  in  details  to  perform  the  heavier 
work.  Instead  of  three  pole-pieces  on  the  armature,  a  large  number  are  used,  which 
are  very  small  in  size,  the  windings  being  placed  between  these  small  poles  or  teeth. 
The  field  contains  perhaps  four  or  more  pole-pieces  with  windings  on  each.  Alter- 
nating current  motors  differ  from  the  direct  current  type  which  we  have  mentioned, 
and  more  about  their  operation  will  be  stated  later. 

Motors  of  the  direct  current  type  are  classified  as  follows,  according  to  the 
connections  of  the  field  winding: 

A  series  motor  is  one  in  which  the  field  winding  is  connected  in  series  with  the 
armature  as  shown  in  the  illustration.  This  type  is  the  usual  one  for  small  motors, 
and  also  the  motors  for  railroad  work.  A  series  motor  can  be  started  with  full  load, 
and  will  easily  gain  its  full  speed  under  such  conditions,  though  the  speed  varies 
considerably  with  the  load,  and  is  never  dependable  for  work  requiring  constant 
speed.  Fig.  3. 

A  shunt  motor  is  one  in  which  the  field  winding  is  connected  across  the  armature, 
which,  in  turn,  is  placed  across  the  power  supply  wires.  This  type  is  the  one  in 
general  use.  It  must  be  slowly  started  but  when  it  has  gained  its  maximum  speed, 
it  maintains  this  speed  fairly  constant  for  varying  loads.  Fig.  4. 

Copyright  1912  by  K.   I.  Co. 


18 


WIRELESS  COURSE— LESSON  NO  3 


The  compound  motor  is  a  combination  of  the  two  foregoing  types,  the  disad- 
vantages of  each  being  largely  overcome,  and  the  advantages  retained.  The  current 
first  passes  through  the  series  field,  and  then  to  the  armature  which  is  connected  in 
series  with  this  field,  and  has  the  shunt  field  connected  across  its  terminals  as  shown 
in  the  diagram.  Fig.  5. 


....  R  ...J 


Series  Wound  Generator. 


Shunt  Wound  Generator. 


Compound  Wound  Generator. 


Fig.  3 


Fig.  4 


Fig.  5 


In  starting  motors  on  high  voltage  circuits  a  form  of  rheostat  must  be  used, 
fig.  6.  This  is  termed  a  "starting  box"  in  the  case  of  a  shunt  or  compound  motor, 
and  consists  of  a  number  of  contacts  mounted  on  a  slate  base  with  a  handle  to  touch 
the  contact,  and  resistance  wire  mounted  on  the  back  of  the  slate  base  and  con- 
nected with  the  contacts.  As  the  handle  is  moved  over  the  contacts,  the  motor 
gains  more  and  more  speed,  until  the  arm  has  reached  the  last  contact  where  a 
stop  prevents  its  further  movement.  An  electromagnet  immediately  attracts  an  iron 
bar  on  the  arm,  and  holds  the  arm  at  the  last  contact.  The  electromagnet  is  connected 
across  the  line  and  holds  the  arm  while  current  is  passing  through  the  motor.  Should 
the  current  fail  or  be  shut  off,  the  motor  will  continue  to  revolve  for  a  few  moments, 
and  the  current  generated  in  its  armature  will  be  sufficient  to  hold  the  arm  to  the  elec- 
tromagnet. However,  as  the  motor  slows  down,  the  electromagnet  releases  the  arm 
which  is  forced  by  a  spring  to  return  to  the  first  contact  and  thus  cut  off  the  line  from 
the  motor.  Now  should  the  current  be  again  turned  on,  the  motor  will  be  safe  as  it 
has  been  automatically  disconnected.  Otherwise  if  such  a  device  did  not  release  the 
arm,  the  motor  would  come  to  a  stop  on  the  failure  of  the  current,  and  when  current 
was  again  turned  on,  the  armature  would  probably  be  ruined  or  badly  damaged  by  the 
rush  of  current,  due  to  the  fact  the  motor  would  not  be  producing  any  counter  E.  M. 
F.  This  electromagnet  is  termed  "no-voltage  release"  and  starting  boxes  equipped 
with  them  are  styled  "automatic."  To  start  a  motor  equipped  with  a  starting  box,  the 
switch  controlling  the  current  is  first  turned  on,  and  then  the  arm-  is  moved  slowly, 
waiting  till  the  armature  has  attained  the  maximum  speed  on  each  contact  before  the 
arm  is  moved  to  the  next  contact.  When  the  motor  is  to  be  stopped,  the  switch  is 
opened  and  the  motor  will  come  to  a  stop.  Care  should  be  taken  to  see  that  the  arm  has 
been  released  before  starting  a  motor,  for  the  failure  of  the  arm  to  return  may  cause 
damage  to  the  motor.  By  covering  the  pole  pieces  of  the  electromagnet  with  thin 
paper  its  failure  to  operate  can  often  be  prevented. 

To  increase  the  speed  of  a  motor,  the  field  is  weakened  by  inserting  resistance.  A 
special  form  of  variable  resistance  consisting  of  an  iron  frame  containing  many  turns 
of  german  silver  or  other  resistance  wire  and  having  a  handle  which  makes  contact  with 
contact  buttons  connected  to  different  points  on  the  wire  is  used,  and  is  termed  a 
"rheostat."  By  turning  the  handle,  more  or  less  resistance  is  introduced  into  the 
shunt  field  winding,  and  the  speed  thus  varied,  the  more  resistance  inserted,  the  higher 
the  speed. 

A  dyamo  is  built  upon  the  same  principles  as  the  motor,  and  the  student  will  re- 
member that  a  wire  cutting  the  lines  of  a  powerful  magnetic  field  causes  an  electro- 
motive force  to  be  generated  in  that  wire  and  if  the  wire  forms  part  of  a  closed  circuit 
a  current  will  flow  through  it.  This  is  the  action  of  the  dynamo.  The  dynamo  also  has 
the  armature  and  commutator,  the  windings  in  the  armature  cutting  the  magnetic 
lines  of  force  and  generating  current.  This  current  is  actually  alternating  current, 
but  is  rectified  to  direct  current  through  the  action  of  the  commutator.  Most  dyna- 
mos may  be  used  as  motors,  and  likewise  some  motors  may  be  used  as  dynamos,  so 
that  the  student  may  readily  see  that  the  details  are  practically  the  same.  An  al- 
ternating current  dynamo  embodies  the  same  principles,  but  has  two  brass  rings  on 


WIRELESS  COURSE— LESSON  NO  3 


19 


the  end  of  the  armature  shaft  in  place  of  the  comutator,  with  two  brushes  pressing  on 
same.  These  brass  rings  are  termed  collector  or  slip  rings. 

The  voltage  of  a  direct  current  dynamo  at  a  given  speed  may  be  varied  by  chang- 
ing the  current  in  the  field  winding.  This  is  accomplished  by  means  of  a  rheostat 
usually  mounted  on  the  switchboard.  The  speed  may  also  be  raised  with  a  correspond- 
ing increase  in  the  voltage.  Dynamos,  as  in  the  instance  of  motors,  are  made  in 
three  types,  series,  shunt,  and  compound.  A  fourth  type  sometimes  employed,  is 
separately  excited,  which  consists  in' having  the  current  for  the  field  supplied  by  some 
external  source  of  current,  such  as  a  battery,  or  generator.  A  small  direct  current 
generator  is  often  mounted  on  the  same  shaft  as  the  armature  of  an  alternating  cur- 
rent dynamo,  and  serves  the  purpose  of  furnishing  the  field  winding  with  direct  current. 
Of  the  various  types,  the  shunt  is  the  most  common  for  charging  storage  batteries 
etc.,  or  where  the  load  is  constant,  while  the  compound  type  is  used  where  the  volt- 
age must  be  kept  constant  with  a  varying  load.  In  alternating  current  installations, 
the  generators  must  be  separately  excited  with  direct  current  inasmuch  as  the  alter- 
nating current  is  not  suitable  for  this  purpose. 

In  changing  alternating  current  to  direct  current,  or  direct  current  to  alternating 
current,  a  motor  directly  coupled  to  a  generator  on  a  common  base  is  used  and  is  known 
as  a  motor-generator  set.  The  motor  is  operated  on  the  current  which  is  to  be  con- 
verted. In  wireless  telegraphy  where  a  transformer  is  used  and  only  direct  current  is 
available,  the  direct  current  operates  the  motor  of  a  motor-generator  set,  while  the 
generator  supplies  the  alternating  current. 

A  simpler  form  of  this  combination  is  the  rotary  converter,  whiuh  consists  of  a 
single  machine  having  slip  rings  at  one  end  of  its  armature,  and  the  usual  commutator 
at  the  other  end. 


MOTOR 


5W/TCH 


COLLECTOR 


START/KG  BOX 


Fig.  6 


POWER  TRANSMISSION  AND  WIRING. 

From  the  generator  in  the  power  station,  the  leads  are  brought  to  a  switchboard, 
which  contains  the  voltmeters,  and  ammeters,  as  well  as  all  the  rheostats  and  other 
controlling  devices.  The  switchboard  is  the  "brain"  of  the  entire  power  station,  for  it 
is  the  controlling  center  for  all  the  machinery  and  distribution  of  current.  From  the 
switchboard  the  wires  pass  out  through  tubes  in  the  walls  of  the  station  and  thence 
to  the  consumers  of  the  current. 

In  the  country,  overhead  construction  is  employed,  as  it  is  comparitively  inexpen- 
sive as  compared  with  the  underground  distributing  systems  employed  in  large  cities. 
The  overhead  system,  however,  possesses  a  number  of  disadvantages,  the  damage  from 
storms,  and  the  objectional  appearance  being  among  the  most  important. 


20 


WIRELESS  COURSE— LESSON  NO  3 


From  the  porcelain  or  composition  tubes  through  the  walls  of  the  power  station, 
Fig.  7,  the  wires  pass  to  the  insulators  on  the  cross  arms  of  the  poles.  If  the  cur- 
rent is  direct  current  and  of  a  suitable  voltage  for  power  and  lighting  purposes,  the 
leads  to  the  various  buildings  are  taken  off  the  nearest  wires,  these  leads  passing 
through  por.celain  tubes  or  iron  pipes  and  into  the  house.  The  leads  are  then  con- 
nected to  a  fuse  block,  which  usually  consists  of  a  porcelain  base  with  suitable  screw 
parts  mounted  on  same,  fig.  8.  Into  these  screw  parts  are  placed  porcelain  plugs 
which  have  a  metal  screw  portion  to  fit  the  thread  of  the  parts  in  the  porcelain  base. 
Each  plug  contains  a  fine  wire  which  connects  the  screw  portion  with  a  contact  button 
on  the  bottom,  the  wire  being  protected  by  a  mica  window.  The  porcelain  base  is 
known  as  a  fuse  cut-out,  and  the  plugs  as  fuse-plugs. 


Fig.  7 

The  purpose  of  the  fuse  wire  is  to  protect  the  circuit  beyond  the  fuse  block  from 
heavy  accidental  currents.  Fuse  wire  is  composed  of  an  alloy,  of  tin,  lead  and  other 
metals,  which  melts  at  a  low  temperature.  Fuses  and  fuse  wire  are  rated  at  the  current 
which  will  cause  the  wire  to  melt.  On  plug  fuses  the  number  of  amperes  is  stampd  on 


Fig.  9 


the  bottom  contact  button,  or  on  the  rim,  while  in  fuse  wire,  the  rated  ampere  capa- 
city is  marked  on  the  containing  spool.  Another  type  of  fuse  usually  employed  for 
power  purposes  is  the  cartridge  fuse.  This  consists  of  a  fibre  tube,  with  metal  parts 
for  the  connections  at  both  ends  and  containing  fuse  wire  which  connects  both  metal 


WIRELESS  COURSE— LESSON  NO  3  21 

parts  within  the  tube  and  is  surrounded  by  asbestos  powder  which  quickly  extin- 
guishes the  arc  formed  and  protects  the  fibre  tube  from  being  blown  to  pieces.  In 
the  plug  fuses  the  mica  window  permits  an  examination  of  the  fuse  wire,  so  as  to  de- 
termine whether  it  has  been  melted  or  "blown  out,"  while  in  cartridge  fuses  the  label 
contains  a  device  to  indicate  when  the  fuse  has  been  melted.  Fuses  should  be  used  in 
all  instances  where  apparatus  is  operated  on  10  volts  or  more,  or  on  storage  batteries 
to  protect  the  apparatus  and  wiring  against  sudden  heavy  currents  which  might  cause 
damage. 

From  the  fuse  block  the  leads  are  usually  brought  to  the  recording  watt-hour 
meter,  which  records  the  amount  of  power  used  by  the  consumer.  In  certain  locali- 
ties, where  cheap  electric  power  is  available  through  the  use  of  water  supply,  the  cur- 
rent is  charged  to  customers  by  the  month,  based  on  a  fixed  number  of  lamps.  An 
accurate  switch  automatically  shuts  off  the  current  or  flashes  the  lights  when  a  sin- 
gle lamp  or  more  are  used  in  excess  of  the  contracted  number,  controls  the  current, 
protecting  the  company  from  fraud.  However,  to  return  to  the  watt-hour  meter 
more  generally  used,  we  find  that  it  operates  on  the  same  principles  as  the  motor,  the 
inside  construction,  Fig.  9,  consisting  of  a  small  armature  turning  on  jewelled  bear- 
ings and  with  a  small  silver  commutator  and  brushes.  A  field  winding  exerts  a  mag- 
netic field  in  which  the  armature  rotates  the  field  flux  being  in  proportion  to  the  cur- 
rent used;  the  field  coils  being  connected  in  series  with  the  circuit.  The  armature, 
being  supplied  with  current  in  shunt  with  the  power  circuit,  rotates  in  proportion  to 
the  voltage  used,  and  is  connected  through  a  series  of  gears  to  pointers  which  indicate 
on  dials  the  number  of  watt-hours  of  energy  consumed.  On  the  bottom  of  the 
armature  shaft  a  copper  or  aluminum  disc  is  fixed  which  rotates  with  the  armature 
and  passes  between  the  poles  of  three  powerful  permanent  magnets.  The  Eddy  cur- 
rents in  the  disc  retard  the  rotation  of  the  armature,  so  that  by  moving  the  magnets 
nearer  to  the  edge  of  the  disc  more  drag  and  more  retardation  can  be  secured.  Thus 
the  speed  can  be  accurately  regulated  so  as  to  coincide  with  the  readings  of  a  stahdard 
watt-hour  meter. 

There  are  five  dials  on  the  common  watt-hour  meter,  these  dials  being  respec- 
tively marked  from  left  to  right,  10,000,000,  1,000,000,  100,000,  10,000,  and  1,000.  These 
figures  represent  the  number  of  watt-hours  represented  by  one  complete  revolution 
of  the  individual  pointer  on  each  dial.  Each  dial  is  marked  from  1  to  0  which  repre- 
sent tenth  parts  of  a  complete  revolution.  One  complete  revolution  of  the  dial  on  the 
extreme  right  marked  1,000,  will  cause  the  neighboring  dial  to  the  left  to  indicate  1 
on  its  dial,  and  so  on.  The  reading  is  therefore  taken  by  noting  the  readings  from 
the  first  dial  to  the  left  to  the  last  dial  to  the  right.  In  order  to  determine  the  current 
consumed  during  a  definite  period  of  time,  it  is  necessary  to  know  the  reading  of  the 
meter  at  the  beginning  of  the  period,  and  this  figure  is  subtracted  from  the  last  read- 
ing at  the  expiration  of  the  period,  thus  giving  the  number  of  watt-hours  for  the 
period  Between  both  readings. 

From  the  meter  the  current  is  conveyed  to  the  various  fixtures  and  appliances. 
In  dry  locations  this  wiring  is  often  placed  in  wooden  moulding  which  has  suitable 
grooves  to  hold  the  wire.  After  t'he  wiring  is  in  the  grooves,  a  covering  commonly 
named  "capping"  is  nailed  over  the  moulding.  In  places  where  there  is  considerable 
moisture  such  as  cellars  or  porches  of  houses,  cleat  wiring  is  employed,  which  consists 
of  running  the  wires  between  porcelain  blocks  spaced  at  every  four  feet.  Two  screws 
pass  through  the  two  cleats  and  the  wire  is  secured  between  the  jaws  of  both 
blocks.  Knob  wiring  is  also  employed,  which  consists  of  using  porcelain  knobs 
in  place  of  cleats,  the  both  wires  being  individually  supported  on  a  separate  row 
of  knobs.  In  houses  where  the  wiring  is  concealed  iron  piping  is  passed  between 
the  floors  and  walls,  this  piping  being  known  as  conduit.  At  regular  intervals  where 
fixtures  are  to  be  placed,  an  iron  box  is  inserted  between  the  lengths  of  the  piping, 
these  boxes  being  named  outlet  boxes.  The  wires  pass  through  the  outlet  box  and 
again  into  the  next  length  of  piping,  so  that  the  wires  must  be  scraped  and  the 
connections  for  the  fixtures  soldered  on  each  wire  which  is  carefully  covered  with 
tape  afterwards.  For  short  stretches  or  where  it  is  desired  to  run  a  line  for  heavy 
current,  steel  armored  but  flexible  tubing  containing  the  wires  firmly  imbeded,  is 
employed,  this  being  known  to  the  electrical  trade  as  "BX."  It  is  especially  recom- 
mended for  carrying  the  current  from  the  cellar  where  the  meter  and  fuse  cut- 
out are  located,  to  the  upper  floors  where  a  wireless  station  is  to  be  operated.  The 
BX  is  fastened  to  the  walls  by  means  of  iron  strips  which  firmly  clamp  it  and  are 
usually  known  as  "straps." 

In  the  cities,  the  electric  feeders  are  placed  underground  in  conduits.  At  con- 
venient intervals  small  rooms  are  placed  under  the  street  and  can  be  reached 
through  a  hole  in  the  street  which  is  normally  covered  with  an  iron  lid,  the  entire 
structure  being  termed  a  "man  hole,"  fig.  10.  On  the  walls  of  these  rooms  are 
the  many  cables,  supported  on  iron  racks,  which  pass  from  one  section  of  the  conduit 
to  the  next  section,  and  thereby  allow  a  workman  to  examine  and  test  the  different 
cables  as  well  as  to  allow  new  cables  to  be  passed  through  the  conduit  or  old  cables 
removed.  From  the  conduits  the  leads  are  brought  into  the  houses  through  the 
cellars  where  connections  are  made  to  the  cutout  and  the  meter.  From  the  meter 
the  same  wiring  as  previously  described  is  used. 

In   alternating   current   transmission,    the   voltage    is    often    far   above    that   which 


22 


WIRELESS  COURSE— LESSON  NO  3 


Fig.  10 

may  be  used  for  lighting  and  power  purposes,  the  reason  being  that  the  lower  the 
amperage  and  the  higher  the  voltage,  the  less  copper  is  needed  in  the  conductors 
and  thus  a  large  saving  in  the  construction  of  the  line  is  accomplished.  This  is 
analogous  to  an  instance  where  water  represents  electricity  and  a  pipe  represents 
the  wire,  and  a  certain  quantity  of  water  measured  by  gallons  must  be  passed  through 
the  pipe  to  be  delivered  at  the  other  end.  Now,  if  we  employ  a  powerful  pressure 
to  force  the  water  through,  a  small  pipe  may  be  used,  but  if  we  employ  a  large 
quantity  of  water  with  little  pressure  behind  it,  a  large  pipe  must  be  employed  to 
obtain  a  suitable  amount  of  water  at  the  other  end.  The  pressure  illustrates  the 
voltage  which  is  applied  to  force  a  greater  current  through  a  smaller  wire.  There- 
fore, in  alternating  current  the  voltage  is  usually  as  high  as  possible  in  order  to  gain 
the  advantage  of  using  smaller  copper  conductors.  In  overhead  construction  the 
student  has  probably  noticed  iron  boxes  on  the  poles  at  intervals  and  did  not  know 
the  purpose  of  these  boxes.  These  boxes  are  transformers,  fig.  11,  and  contain  two 


Fig.  11 

windings,  the  primary  being  connected  to  the  power  supply  while  the  secondary 
is  connected  to  the  consumer's  wiring.  The  transformer  is  of  the  closed  core  type, 
and  has  very  high  efficiency,  usually  ranging  between  92  and  98  per  cent.  It  is 
termed  a  step-down  transformer,  since  the  voltage  is  stepped  down  in  this  instance. 
The  current  of  the  line  is  thus  lowered  to  a  suitable  voltage  which  the  consumer  can 
employ,  so  that  the  advantage  gained  in  employing  high  voltage  does  not  cause 
any  inconvenience  to  the  consumer.  The  transformer  can  also  be  used  to  step  up  the 
current.  For  instance,  if  for  reasons  of  safety  a  low  voltage  can  only  be  sent  through 
the  wire,  the  tension  can  be  increased  or  stepped  up  by  the  use  of  a  transformer 
to  any  voltage  desired  at  the  place  where  it  is  to  be  used. 

If  the  transformer  is  to  be  used  to  step  up  a  current,  the  secondary  winding 
has  more  turns  of  wire  than  the  primary,  and  vice  versa,  if  the  current  has  to  be 
stepped  down,  the  primary  has  more  turns  of  wire  than  the  secondary.  Figs.  12 
and  13  are  hook-ups  of  transformers  connected,  in  series  and  in  parallel. 


WIRELESS  COURSE— LESSON  NO  3 


23 


Alternating  current  is  gaining  in  favor  over  direct  current  for  power  transmis- 
sion, and  it  is  probably  a  matter  of  only  a  few  years  before  it  will  be  extensively 
used  and  will  supercede  direct  current  in  all  transmissions  of  any  reasonable  distance. 

Alternating  current  motors  are  of  various  types,  which  would  occupy  more 
space  to  describe  than  this  course  permits,  but  it  is  important  to  know  that  the  most 
common  type  in  small  sizes  is  the  induction  motor.  This  type  consists  of  a  number 
of  iron  poles  with  field  windings,  mounted  on  the  motor  frame,  the  windings  being 
connected  to  the  power  supply.  The  moving  member  is  not  named  an  "armature" 
but  is  known  as  the  rotor.  The  stationary  winding  is  called  the  stator.  It 
consists  of  many  punched  discs  which  are  insulated  with  varnish  and  mounted  together 
on  a  steel  shaft.  In  suitable  grooves  in  these  discs  are  heavy  copper  wires  which 
are  connected  together,  though  they  have  no  connection  with  the  current  supply.  The 
action  of  the  motor  is  therefore  based  on  induction  effects  in  these  windings  and  in 
the  iron  discs,  causing  the  rotary  movement.  There  are  other  types  besides  the  induc- 
tion, notably  the  slip  ring  type  which  is  extensively  used. 


Fig.  12 


Fig.  13 


Alternating  current  differs  from  direct  current  as  already  stated,  by  the  fact 
that  it  changes  its  polarity  at  regular  intervals.  At  one  instant  a  wire  carrying  an 
alternating  current  will  be  the  positive  pole  while  at  the  next  instant  it  will  be  the 
negative  pole.  The  current  begins  at  O  voltage  and  rises  to  the  maximum  positive 
voltage  and  then  descends  to  O,  but  immediately  begins  to  arise  to  the  maximum 
negative  voltage  and  then  descends  to  O,  which  may  be  noticed  in  the  diagram, 


Fig.  14 

fig.  14,  where  the  straight  center  line  represents  time  elapsed,  and  also  O  potential. 
One  complete  period  in  which  the  maximum  potentials  in  both  polarities  have  been 
reached  is  termed  a  cycle.  Alternating  current  is  always  specified  in  cycles,  as 
this  constitutes  an  important  item  which  is  needed  in  the  furnishing  of  proper  apparatus 
and  machinery  to  operate  on  this  current.  Standard  power  circuits  employ  either  25 


24  WIRELESS  COURSE— LESSON  NO  3 

or  60  cycles  and  lighting  circuits  60,  125  and,  in  some  instances,  133  cycles,  per  second. 
An  alternation  is  half  of  a  cycle,  and  represents  the  rise  and  fall  of  one  potential 
cycle.  The  frequency  is  the  number  of  cycles  per  second,  and  usually  is  employed 
in  connection  with  the  number  of  cycles,  thus,  if  a  motor  is  said  -to  operate  on  a 
frequency  of  60  cycles,  it  means  that  the  motor  will  operate  on  an  alternating  cur- 
rent having  60  cycles  per  second.  If  frequency  is  not  mentioned  in  connection  with 
cycles,  the  meaning  is  lost.  In  the  diagram  the  relation  of  the  terms  may  be 
clearly  seen,  the  alternation  being  from  A  to  B  or  from  B  to  C,  and  the  cycle  from 
A  to  C. 

In  some  power  transmissions,  a  number  of  cycles  may  be  employed  at  the  same 
time,  and  thus  when  one  cycle  is  rising  towards  its  maximum  positive  voltage,  the  next 
cycle  is  just  beginning,  while  a  third  cycle  may  just  have  passed  through  half  of  its 
period.  Each  one  of  these  separate  cycles  are  termed  phases,  a  single  phase  line 
being  one  in  which  only  one  definite  cycle  exists,  while  in  a  two  phase  line  there 
are  two  cycles  at  the  same  instant,  and  in  a  three  phase  line  there  are  three  cycles 
at  the  same  instant.  The  study  of  these  complicated  forms  of  current  transmis- 
sion may  be  thoroughly  covered  by  referring  to  text  books  which  cover  the  electrical 
engineering  field,  but  this  passing  word  is  all  that  can  be  mentioned  in  the  limited 
space  of  this  course. 

In  direct  current  transmission,  a  method  of  great  convenience  and  representing 
a  62^%  saving  in  copper  is  largely  used,  and  known  as  the  Edison  three  wire  system, 
fig.  15.  Two  110  volt  generators  are  connected  in  series  across  two  wires  so  that  the 
voltage  on  these  leads  will  be  220  volts.  From  the  connection  between  the  two 
generators,  another  lead  is  taken  so  that  by  connecting  to  this  lead  and  one  of  the 
other  leads  a  voltage  of  110  volts  is  obtained  since  the  current  of  only  one  generator 
is  being  used.  Thus  the  consumer  may  use  either  110  or  220  volts  according  to 
the  work  he  has.  By  using  220  volts  a  considerable  saving  is  effected  in  the  two 
outside  leads  and  the  common  return  is  used  for  both  circuits  furnishing  110  volts, 
saving  the  cost  of  a  fourth  independent  wire.  The  center  wire  is  termed  the  neutral 
wire,  and  usually  is  grounded  so  as  to  give  greater  protection  to  consumers.  Great 
care  must  therefore  be  taken  against  accidental  contact  of  either  outside  wire  with 
the  ground  connection  or  with  objects  which  are  connected  with  the  ground,  such 
as  gas,  water,  or  steam  pipes,  for  there  will  be  a  rush  of  current  and  a  blowing  of 
the  fuses.  For  this  reason  it  will  be  noticed  that  all  lighting  fixtures  are  connected 
to  the  gas  pipe,  or  the  fixture  hanger,  through  a  small  insulating  joint  which 
thoroughly  insulates  the  fixture  from  accidental  contact  with  the  ground  should  one 
of  the  wires  touch  the  metal.  All  motors  under  Y$  H.  P.  may  be  \ised  on  110  volts, 
but  those  of  a  higher  power  must  be  used  on  220  volts.  For  this  reason  the  student 
must  bear  in  mind  that  it  is  important  to  examine  a  motor  closely  when  it  is  larger 
than  Y$  H.  P.  and  is  to  be  used  on  a  three  wire  transmission  system,  since  a  110 
volt  motor  would  be  useless  in  this  instance,  due  to  the  Underwriter's  rules. 


o 


THE  ED* <56 W  THREE  W/RE  SYSTEM. 


Fig.  15 

After  these  few  lessons,  in  which  the  subject  of  electricity  has  been  but  roughly 
covered,  the  explanations  being  only  to  identify  certain  facts  and  points  as  are  neces- 
sary to  understand  .the  complicated  apparatus  and  operations  of  the  wireless  tele- 
graph and  telephone,  the  next  lesson  begins  the  principles  of  wireless  telegraphy 
with  the  succeeding  lessons  leading  through  a  complete  and  thorough  study  of  the 
subject  to  which  this  course  is  devoted. 


WIRELESS  COURSE— LESSON  NO.  4 


25 


Lesson  Number  Four. 

THE  PRINCIPLES  OF  WIRELESS  TELEGRAPHY. 

'••rHE   explanation   of   the   principles   of  wireless   telegraphy   to   the   layman    would 
i\V      be  a  difficult  problem  if  a  comparison  with  the  waves  of  a  body  of  water  were 
^^      not    possible.     Fortunately,    however,    we    can    make    an    interesting    analogy 
between  water  and  wireless  waves  as  in  the  previous  study  of  elementary  electricity. 
We  will  take  for  instance,  a  body  of  water  30  feet   in  length.     At  the  two  oppo- 
site banks,  small  platforms  have  been   built  as  illustrated  in  fig.   1.     On  one  of  these 


Fig.  1. 


platforms,  a  large  paddle  has  been  arranged  so  that  a  person  may  operate  its  handle. 
Now,  if  the  paddle  is  moved  back  and  forth,  a  series  of  waves  extending  in  all 
directions  from  this  source  of  creation,  will  be  formed.  The  waves  spread  further 
and  further  away  from  the  paddle  in  concentrical  rings  until  their  strength  is  com- 
pletely expended.  In  this  instance,  the  pond  is  small  and  the  waves  are  sufficiently 
powerful  to  reach  the  opposite  bank  whereon  the  other  platform  is  built. 

On  the  other  platform,  located,  on  the  opposite  shore,  we  have  a  smaller  paddle, 
on  the  handle  of  which  a  hammer  hitting  against  a  gong,  has  been  arranged.  It  is 
obvious  that  the  waves  moving  the  paddle  will  cause  the  gong  to  ring,  informing 
the  operator  on  that  platform  that  the  operator  on  the  other  platform  is  moving 
the  paddle  and  creating  waves  on  the  surface  of  the  water.  By  skillful  manipula- 
tions of  the  larger  paddle,  it  is  possible  to  cause  the  smaller  paddle  to  ring  the 
bell  periodically  as  desired,  and  if  a  series  of  signals  have  been  prearranged,  the 
operator  with  the  larger  paddle  may  communicate  certain  information  by  properly 
operating  its  handle.  This  represents  both  the  transmitting  and  receiving  stations 
of  the  wireless  telegraph,  the  larger  paddle  being  the  transmitter,  and  the  conducting 
medium  being  the  water,  while  the  smaller  paddle  is  the  receiver. 

In  the  actual  wireless  telegraph  system,  we  find  the  same  essentials.  The  ether 
is  the  conducting  medium,  the  Hertzian  waves  are  the  means  of  communication,  and 
the  codes  are  the  prearranged  signals.  The  paddles  correspond  to  the  "aerials"  in 
the  actual  wireless  system,  since  aerials  both  impart  and  intercept  the  waves  travel- 
ling through  the  ether. 

The  ether  or  conducting  medium  in  wireless  telegraphy,  is  little  understood  at 
the  present  lime.  It  is  a  substance  which  fills  all  spaces  not  already  occupied  by 
other  substances.  It  exists  everywhere;  between  planets,  suns,  in  nature,  and  even 
in  the  pores  of  metals,  wood,  and  other  substances.  It  is  comparable  to  water 
soaking  into  a  sponge,  since  it  occupies  every  pore  in  the  universe  not  occupied  by 
another  substance. 

After  the  theory  of  Maxwell,  ether  is  also  the  medium  of  the  electrical  pheno- 
menon, since  each  particle  of  ether  assumes  a  peculiar  state  of  electricity,  in  which 
one  end  of  the  particle  assumes  a  negative  electric  charge  while  the  other  end  assumes 
a  positive  charge,  the  two  charges  being  seemingly  separated  by  an  exterior  influence. 
The  difference  in  polarity  between  adjoining  particles  causes  them  to  group  together 
firmly,  so  that  a  foreign  disturbance  can  force  them  slightly  apart,  but  after  remov- 
ing this  force  the  particles  again  come  together.  The  action 'of  the  exterior  elec- 
trical force  is  to  cause  the  adjoining  particles  to  become  charged  with  the  same 
polarity,  which  causes  the  particles  to  draw  apart.  When  the  electrical  force  is 
removed  the  particles  are  again  in  the  same  electrical  state  as~  before,  with  the 
result  that  they  come  together  again. 

In  1888.  a  young  German  scientist,  Heinrich  Rudolf  Hertz,  set  forth  in  a  writteTi 
statement,  a  series  of  interesting  experiments  in  which  remarkable  characteristics 
of  electro-magnetic  waves  were  discussed.  These  waves  have  since  been  named 
Hertzian  waves,  in  honor  of  the  researches  performed  by  Hertz.  The  waves  were 
produced  by  connecting  to  the  terminals  of  a  spark  coil  two  brass  balls  mounted 
on  rods,  these  rods  having  little  metal  squares  at  the  extremeties,  or  if  desired,  the 
ends  of  the  rods  may  be  bent,  serving  the  same  purpose.  This  arrangement  is  known 

rnpyrijrht  1912  b.v    K    I    O« 


26 


WIRELESS  COURSE— LESSON  NO.  4 


as  the  Hertz  radiator  or  oscillator,  and  is  illustrated  in  fig.  2.  When  the  current  was 
supplied  to  the  spark  coil,  a  discharge  passed  between  the  brass  balls.  When  a  loop 
of  heavy  wire  with  a  small  gap  left  between  the  ends  of  the  spiral  was  brought 
in  the  neighborhood  of  the  oscillator,  small  sparks  were  noticed  to  jump  across  the 
gap  of  this  spiral,  proving  that  the  electro-magnetic  waves  had  been  generated  and 
propogated  through  the  intervening  space  or  etner.  This  loop  is  known  as  tire  Hertz 
resonator  or  receiver  and  is  shown  in  fig.  3.  Those  electro-magnetic  waves,  caused  by 
the  discharge  of  a  high  tension  electric  current,  are  similar  to  light  rays  in  certain 
characteristics,  and  they  may  be  reflected,  deflected,  gathered,  and  dispersed  by 
metal  'screens.  Differing  from  light  rays  in  other  respects,  they  will  penetrate 
without  difficulty  stone,  wood,  earth,  and  other  non-metallic  material,  which  are 
unpenetrable  by  light  rays. 

Thus  the  principle  of  wireless  telegraphy  is  based  on  the  fact  that  an  electrical 
discharge  may  be  employed  for  generating  electro-magnetic  waves  which  travel 
through  space  in  all  directions  from  the  source  of  production.  It  is  also  known 
that  these  electro-magnetic  waves  can  produce  effects  in  conductors  placed  within 
the  range  of  the  waves.  The  problem  therefore  consisted  of  perfecting  means  of 
detecting  these  waves,  and  to  increase  the  efficiency  and  distance  possible  to  create 
these  results  with  a  reasonable  amount  of  electrical  energy  in  the  spark  coil. 


Fig.  2 


Fig.  3 


In  1894,  Professor  A.  Rhigi  of  Italy,  made  interesting  experiments  along  the 
same  lines  as  his  predecessor  Hertz,  but  used  perfected  apparatus  of  his  own.  His 
resonator  consisted  of  a  glass  sheet  upon  which  copper  had  been  deposited  in  a 
strip.  This  strip  was  scratched  with  a  sharp  razor  blade,  so  that  a  minute  spark  gap 
was  formed  between  the  two  separated  halves  of  the  copper  strip.  By  placing  the 
gap  under  a  powerful  microscope,  the  almost  invisible  sparks  could  be  seen.  This 
resonator,  of  course,  proved  to  be  far  more  practical  than  the  Hertz  resonator, 
and  much  greater  distances  were  covered. 

The  early  experimenters  perceived  the  possibility  of  using  these  waves  for 
transmitting  energy  across  space  without  connecting  wires,  and  steady  progress 
was  made  towards  perfecting  the  apparatus.  In  1866,  S.  A.  Varley  had  discovered 
that  the  high  electrical  resistance  of  metal  filings  might  be  greatly  decreased 
by  the  passing  of  an  electrical  discharge  through  them,  and  on-  being  shaken,  the 
original  high  resistance  was  regained.  In  1884,  Calzecchi-Onesti  also  discovered 
that  the  high  electrical  resistance  of  filings  could  be  thus  effected,  and  wrote* on 
his  experiments  and  discoveries. 

In  1890,  Professor  E.  Branly  of  the  University  of  Paris,  rediscovered  the  inter- 
esting action  of  filings,  but  placed  these  in  a  glass  tube  with  metal  plugs  fitting 
in  on  both  sides,  thereby  making  electrical  connections  with  the  filings.  He  dis- 
covered that  even  discharges  at  a  distance  from  the  filings  created  the  same  effect, 
though  the  actual  discharge  did  not  pass  through  the  filings.  To  the  tube  he  gave  the 
name  of  "radio-conductor." 

The  following  information  describes  the  principle  upon  which  the  Branly  cqherer 
operates.  As  the  resistance  between  the  filings  in  such  a  coherer  is  extraordinarily 
high,  amounting  to  several  hundred  ohms,  the  current  from  a  battery  cannot  possibly 
flow  through  the  filings.  But,  upon  the  receipt  of  a  high  frequency  current  wave, 
minute  sparks  jump  between  the  filings  and  cause  the  neighboring  filings  to  be 
slightly  fused  together.  The  electrical  contact  between  the  filings  is  immediately 
improved,  and  the  resistance  decreases  to  about  5  to  10  ohms.  The  same  battery 
as  previously  mentioned  which  was  unable  to  pass  a  suitable  current  strength 
through  the  coherer,  can  now  send  a  very  powerful  current  through  the  cohered 
filings  and  operate  the  relay. 

In  1893  and  1894,  Sir  Oliver  Lodge  applied  the  Branly  tube  in  place  of  a  micro- 
meter spark  gap  on  thjs  Hertz  resonator,  and  gave  the  name  of  "coherer"  to  the 
filings  tube.  The  terminals  of  the  coherer  were  connected  to  a  galvanometer  and 


WIRELESS  COURSE— LESSON  NO.  4 


27 


powerful  battery,  and  the  tube  could  be  shaken  or  tapped  by  means  of  a  clockwork 
mechanism  or  an  electrical  bell.  With  the  reception  of  the  Hertzian  waves  the 
coherer  operated  and  allowed  the  battery  current  to  deflect  the  galvanometer.  The 
clockwork  or  electrical  bell  was  then  employed  to  decohere  the  filings  and  to  return 
them  to  the  original  high  resistance  state.  The  maximum  distance  obtained  with 
this  apparatus  was  55  yards  from  the  transmitter. 

In  1895,  Professor  Popoff  employed  the  nearest  approach  to  .the  present  day 
receiving  outfit.  To  each  terminal  of  a.  coherer,  he  connected '  respectively  a  wire 
leading  to  the  ground,  and  a  wire  supported  on  a  high  pole  outside  the  build- 
ing, and  corresponding  to  the  aerials  of  the  present  day  systems.  Shunted  across 
the  coherer  was  a  relay  and  battery,  while  the  relay  contacts  operated  an  electric 
bell  which  tapped  against  the  coherer  tube.  The  apparatus  was  used  with  success 
to  register  the  discharges  of  lightning  at  great  distances. 

In  1896,  G.  Marconi  began  his  early  experiments  which  finally  led  to  the  per- 
fection of  the  present  day  commercial  systems.  At  the  transmitting  end  a  spark 
coil  with  the  Hertz  oscillator  as  shown  in  fig.  2  was  employed,  while  the  receiving 
end  contained  a  coherer  and  decoherer  similar  to  that  shown  in  fig.  4.  At  each 


Fig.  4 


Fig.  5 


discharge  of  the  transmitter  the  coherer  causes  the  bell  to  ring,  which  decohers  the 
filings  the  instant  the  transmitter  stops.  The  adjustment  of  the  coherer  has  to  be 
very  delicate,  since  the  metal  plugs  have  to  be  arranged  until  the  filings  are  correctly 
packed.  If  they  are  tightly  packed,  the  coherer  will  not  operate,  and  if  the  filings 
are  too  loose,  the  action  is  again  spoiled.  While  the  results  obtained  with  the 
ordinary  bell  are  satisfactory,  "much  greater  distances  can  be  obtained  by  using 
a  sensitive  relay  in  place  of  the  bell.  Marconi  soon  adopted  a  high  resistance  and 
sensitive  relay  which  was-  connected  across  the  coherer  in  series  with  the  battery. 
The  bell  was  then  substituted  with  a  delicate  electromagnetic  hammer  which  had 


28 


WIRELESS  COURSE— LESSON  NO.  4 


accurate  adjustments  in  order  to  touch  the  tube  with  the  correct  shaking  necessary. 
The  coherer  was- then  "changed  to  afrbther  type  (fig.  5)  where  the  whole  tube  was 
sealed  with  the  wires  coming  through  both  ends,  the  interior  of  the  tube  having- 
been  exhausted  of  its  air.  The  metal  plugs  were  bevelled  across  the  entire  surfaces,  so 
that  by  tilting  the  tube  the  fillings  would  be  either  tighter  or  looser,  depending  how 
the  tube  was  turned.  Fig.  6  illustrates  the  wiring  of  the  earlier  receiving  sets. 

Marconi  soon  discovered  that  by  using  elevated  wires  or  surfaces,  and  grounded 
connections  on  both  the  receiver  and  the  transmitter,  it  was  possible  to  increase 
the  range  considerably,  and  consequently  adopted  these  connections  in  his  later 
experiments.  By  connecting  a  Morse  tape  register  across  the  point  marked  G  in 


Fig.  6 


Fig.  7 


fig.  7,  a  permanent  record  of  the  signals  could  be  kept.  By  'means  of  a  plain  knife 
switch  it  was  possible  to  throw  on  either  the  sending  or  receiving  apparatus  to  the 
aerial  in  order  to  transmit  or  receive,  as  shown  in  fig,  8. 


Fig.  8 


However,  all  the  systems  thus  far  have  been  simply  discussed  in  view  of  the 
fact  that  they  will  receive  and  send  when  operated,  but  the  subject  of  wave  length 
has  not  been  'mentioned.  Electro-magnetic  waves  are  similar  to  those  of  sound 
and  we  will  therefore  make  the  following  analogy.  -If  two  instrument  strings  are 
stretched  at  opposite  ends  of  a  table,  and  one  of  these  strings  is  caused  to  vibrate, 
the  other  string  will  remain  motionless.  However,,  if  the  silent  string  be  carefully 
tuaed  until  it  is  in  harmony  with  the  other  string,  it  will  begin  to  vibrate,  this  action 
being  due  to  the  sound  waves  in  the  air  caused  by  the  vibrating  string.  In  wireless 
telegraphy  the  electro-magnetic  waves  emitted  by  a  transmitter  also  have  a  definite 
•pitch  or  "tune"  as  it  is  named.  It  is  also  referred  to  as  "wave-length."  This  wave- 
length is  caused  by  the  capacity  and  inductance  in  the  circuit  of  either  the  trans- 


WIRELESS  COURSE— LESSON  NO.  4 


29 


mitter  or  the  receiver.  In  the  instance  of  the  Hertz  oscillator  and  resonator,  the 
small  metal  squares  or  rods  at  each  end  of  the  spark  gap  are  adjusted  so  as  to  be 
in  tune  with  the  resonator,  or  tfie  little  squares  or  wire  ends  of  the  resonator  may 
be  adjusted  so  as  to  be  in  tune  with  the  oscillator  waves.  Thus,  in  all  instances, 
two  methods  for  tuning  the  both  stations  may  be  employed,  either  tuning  the 
transmitter  to  the  receiver,  or  the  receiver  to  the"  transmitter.  The  latter  is,  in 
commercial  practice,  generally  used,  as  it  is  more'  practical  than  the  tuning  of 
the  transmitter. 

The  fact  that  electro-magnetic  waves  have  a  definite  wave  value,  has  rendered 
syntonic  or  selective  wireless  telegraphy  possible.  The  simplest  method  employed 
and  applied  to  the  early  Marconi  sets,  is  illustrated  in  fig.  9,  where  there  are  two  sets 
with  aerial  and  ground  connections.  At  the  transmitting  station,  a  coil  containing 
a  number  6~f  turns  of  heavy  wire  and  with  an  adjustable  contact  to  make  connection 


TRANSMITTER 


RECEIVER 


Fig.  9 

for  any  number  of  turns,  is  employed  in  the  aerial  circuit.  This  coil  is  known 
as  the  "helix"  and  will  be  described  in  detail  in  a  later  lesson.  By  adding  more 
or  less  turns,  the  inductance  of  the  aerial  is  varied  and  the  wave-length  altered. 
The  more  inductance  placed  in  the  circuit,  the  greater  the  resultant  wave-lengtft. 

At  the  receiving  end,  inductance  is  likewise  added  in  the  aerial  circuit,  tfius 
giving  the  receiving  cir.ouit  a  greater  wave-length  in  order  to  be  in  tune  with  4he 
transmitter.  In  this  instance,  unlike  the  coil  in  the  transmitter,  many 'turns  of  fine 
wire  are  used,  with  a  sliding  contact  to  make  connections  with  any  turn  desired/ 
This  coil  is>  known^as  the  "tuner"  or  "tuning  coil,"  and  will  be  described  at  length 
:in  a 


30 


WIRELESS  COURSE— LESSON  NO.  4 


Wave-length  is  quoted  in  meters,  which  is  determined  by  means  of  a  calibrated 
instrument  known  as  the  -"wave-meter."  In  the  instance  just  described,  it  has  been 
learned  that  wave-length  may  be  increased  by  adding  more  inductance  in  the  aerial 
circuit.  It  has  also  been  stated  that  capacity  likewise  determines  wave-length. 
In  some  instances,  it  so  happens  that  the  wave-length  of  the  transmitter  is  shorter 
than  that  of  the  receiver,  even  with  no  inductance  turns  in  the  receiving  aerial. 
In  this  instance,  the  following  method  is  employed  in  the  receiving  circuit.  A 
condenser  is  placed  in  the  ground  circuit  as  illustrated  in  the  diagram  of  fig.  10, 
and  thereby  reduces  the  wave-length  of  the  circuit,  through  the  fact  that  capacity 
in  series  decreases  the  to^al  capacity  of  a  circuit.  With  the  circuit  illustrated  in 
fig.  10,  it  will  be  possible  to  tune  in  long  wave-lengths,  and  also  short  wave-lengths, 
by  varying  the  inductance,  or  varying  the  capacity  in  the  ground  circuit.  In  the 
transmitting  circuit,  the  same  proceedure  is  employed,  the  condenser  being  of  the 
leyden  jar  type.  Only  in  rare  instances,  however,  is  such  a  method  employed,  since 
the  transmitting  energy  is  greatly  reduced  through  the  introduction  of  the  ground 
capacity  in  series. 


Fig.  10 


® 


The  various  circuits  outlined  thus  far  are  known.  as-  the-  open  circuit  type;  but 
not  possessing  the  high  degree  of  selectivity  and  efficiency  as  is  possible  to  obtain  in. 
closed  circuits,  Marconi  abandoned  the  open  types  and  began  the  study  of  closed 
types  for  both  receivers  and  transmitters.  These  are  used  to-day  for  all  commer- 
cial work.  The  main  objection  of  the  open  type  of  circuit  is  due  to  the  fact  that 
it  contains  but  slight  capacity,  and  hence  the  resultant  waves  are  highly  damped. 
By  damped  is  meant  that  the  individual  sparks  of  the  transmitter  produces  but  a  single 
trairr  of  waves,  which-  rapidly  diminishes  in  value,  while  an  undamped  wave  is 
one  in  which  the  individual  sparks  produce  a  train  of  waves  where  the  fluctuations 
are  more  persistent  and  detoriate  very  slowly  in  value.  This  may  be  illustrated  by 
a  simple  mechanical  experiment.  If  a  string  of  sufficient  length  is  attached  to'  a 


WIRELESS  COURSE— LESSON  NO.  4 


31 


heavy  weight  at  its  lower  end,  and  allowed  to  swing  back  and  forth,  it  will  swing 
slowly  but  for  a  long  period.  The  length  of  the  string  represents  the  capacity  in 
the  wireless  circuit.  Now,  if  this  same  string  be  suddenly  shortened,  the  weight 
will  swing  much  faster,  but  the  swings  will  rapidly  subside  and  the  swinging  cease. 
This  illustrates  a  wireless  circuit  with  slight  capacity  as  encountered  in  the  open 
circuits.  The  former  instance  with  the  long  string  is  known  as  a  slightly  damped 
circuit  in  the  corresponding  electrical  action,  and  the  latter  is  known  as  a  highly 
damped  circuit  in  the  electrical  equivalent.  Thus  it  will  be  seen  that  a  great 
advantage  exists  in  employing  a  closed  circuit  so  as  to  obtain  the  longer  and 


Fig.  11 

slightly  damped  waves,  which  create  greater  effects '  on  distant  receivers.  The 
comparative  efficiency  of  tuned  closed  circuits  over  open  circuits,  may  be  noticed 
by  the  experiments  of  Marconi,  in  which  it  was  experienced  that  a  tuned  transmitter 
operated  a  tuned  receiver  30  miles  away,  while  the  same  transmitter  did  not  effect 
a  non-tuned  receiver  only  160  feet  away. 

A  great  improvement  in  the  transmitting  apparatus  was  secured  through  the 
use  of  the  closed  circuit,  and  using  condensers,  which  heretofore  had  not  been  used 
with  the  open  circuit  transmitters.  This  permitted  the  full-capacity  effect  to  add 
to  the  lengthening  of  the  waves,  so  that  they  would  be  damped  to  a  minimum.  Fig. 
11  illustrates  a  tuned  transmitter  in  which  it  will  be  noted  that  a  condenser  has 
been  placed  across  the  induction  coil,  while  the  spark  gap  has  been  arranged  in 
series  with  the  inductance  which  is  interposed  between  the  ground  and  the  aerial. 
The  spark  gap  may  also  be  arranged  across  the  induction  coil,  and  the  condenser 
in  series  with  the  inductance;  either  method  of  connection  being  satisfactory.  The 
action  of  this  circuit,  is  the  charging  of  the  condenser  to  its  utmost  capacity,  which 
then  discharges  across  the  gap,  and  the  gap  being  connected  in  series  with  the 
inductance  coil,  it  causes  the  energy  to  surge  through  the  closed  circuit  and  to  be 
radiated  into  the  aerial  and  the  ground.  It  will  be  noted  that  the  connections  of  the 
aerial  may  be  altered  on  the  inductance,  so  that  the  proper  relation  of  wave-length 
may  be  obtained  in  reference  to  the  receiver.  The  closed  circuit,  which  is  termed 
the  "closed  oscillating  circuit,"  is  also  variable,  the  maximum  results  being  obtained 
when  both  the  aerial  and  closed  oscillating  circuits  are  in  perfect  tune,  which  is 
accbmp'lished  by  adding  or  lessening  the  number  of  turns  of  either  circuit. 


©  ^ 


Fig.  12 

The  closed  circuit  receiving  apparatus  likewise  consists  of  a  condenser  and  an 
inductance.  This  method  enables  the  apparatus  to  receive  the  full  advantage  of  the  inter- 
cepted waves,  and  operates  by  the  difference  of  potential  across  the  inductance  coil,  the 
connections  being  illustrated  in  fig.  12.  It  -will  be  noted,  that  a's  in  the  transmitter, 
the  two  circuits  are  separately  tuned,  so  that  perfect  June,  or  resonance  may  exist 
between  the  aerial  and  closed  circuit. 


32 


WIRELESS  COURSE— LESSON  NO.  4 


Both  the  transmitting  and  receiving  circuits  above  described  are  known  as 
closed  'direct  coupled  circuits.  Another  form  of  closed  circuit,  is  knowr.  as  the  induc- 
tive coupled  type,  and  in  which  the  aerial  circuit  is  connected  to  the  ground  through 
a  coil,  while  another  coil  placed  near  the  first  coil,  is  connected  to  the  transmitter 
or  receiver,  the  principle  being  that  of  a  transformer.  By  the  adoption  of  these 
inductive  circuits  (fig.  13),  a  considerable  advancement  over  the  proceeding  systems, 
as  regarding  selectivity  and  efficiency,  has  been  made  possible,  though  at  the  present 
time  the  inductive  coupled  transmitter  is  not  used  as  extensively  as  the  direct  coupled 
type.  However,  in  receiving,  the  inductive  coupled  method  is  much  superior  to  the 
direct  coupled;  the  two  spools  being  suitably  mounted  so  that  one  coil  may  be 
drawn  away  from  the  other  coil,  and  a  greater  or  less  degree  of  coupling  attained. 
.Such  an  instrument  containing  these  two  coils  is  known  as  a  "loose-coupler"  or 
"inductive-tuner." 


RECEIVER 


TRANSMITTER 


Fig.  13 


The  action  of  the  inductance  coils  in  both  the  transmitter  and  the  receiver 
produce  other  effects  besides  the  advantage  of  variable  tuning.  If  an  induction  coil 
be  connected  as  shown  in  fig.  13  to  several  leyden  jars  and  a  spark  gap,  as  well  'as 
a  few  turns  of  heavy  wire  surrounding  a  cylinder  wound  with  many  turns  of  finer 
wire,  we  have  what  is  known  as  the  "Tesla  Coil,"  or  air  core  transformer,  originally 
introduced  by  Nikola  Tesla,  during  1890.  These  two  coils  constitute  an  open  core, 
(air)  transformer,  which  produces  tremendous  high  frequency  and  high  voltage  cur- 
rents at  the  secondary  terminals.  If  a  single  coil  be  used,  containing  many  turns 
of  wire,  and  the  same  induction  coil  and  accessories  be  connected  across  a  few 
turns,  it  will  be  found  that  from  the  two  extreme  ends  of  this  coil,  high  frequency 
current  may  also  be  obtained,  but  the  results  are  not  as  readily  controlled  as  when 
an  entirely  separate  coil  is  used  for  each  circuit.  When  a  single  coil  is  used,  the 
name  of  "auto-transformer"  is  applied  to  the  coil,  but  usually  it  is  known  as  a 
helix  in  regular  practice.  Thus  a  helix  and  a  tuning  coil  are  auto-transformers,  while 
loose-couplers  and  inductive  transmitters,  are  really  Tesla  transformers.  For  the 
preceding  reasons,  it  may  be  noted  that  the  inductively  coupled  circuits  are  preferable, 
due  to  their  greater  range  of  adjustment. 

In  the  receiving  circuits,  the  loose-coupler  not  only  performs  the  mission  of 
tuning  the  apparatus,  but  also  converts  the  intercepted  high  frequency  waves  which 
flow  down  the  aerial  wire,  into  the  high  frequency  currents  of  any  desired  potential, 
which  acts  upon  the  receiving  apparatus.  In  a  later'  lesson  different  types  of  wave 
detecting  devices  will  be  described  and  which  are  known  as  "detectors"  or  cymoscopes. 
Different  dectectors  operate  better  on  different  current. 

Short  wave-lengths  are  more  readily  absorbed  by  obstacles  than  longer  wave- 
lengths. For  most  commercial  work,  the  standard  wave-length  of  425  or  450 
meters  has  been  adopted.  For  long  distance  transmission,  longer  wave-lengths 
are  used  sometimes  as  high  as  5,000  meters.  Over-land  transmission  is  not  practical 
with  short  wave-lengths,  and  usually  a  .wave-length  of  3,000  or  more  is  used  to 
obtain  better  results.  For  the  average  station  of  limited  power,  it  is  impossible  tc 
use  long  wave-lengths,  for  the  transmitter  is  incapable  of  giving  fair  results  witl 
this  huge  •  wave-length.  Most  amateurs  operate  their  transmitters  between  50  and 
300  meters. 


WIRELESS  COURSE— LESSON  NO.  5 


33 


Lesson  Number  Five. 


THE  AMATEUR  TRANSMITTING  SETS  AND  APPARATA. 

~f*  AVING  learned  the  principles  of  wireless  telegraphy,  naturally  the  next  step  in 

liU      t^ie  subject  is  the  thorough  mastering  of  the  transmitting  and  receiving  sets. 

~\       Accordingly,  the  present  lesson  has  been  devoted  to  the  simple  transmitting 

sets  mostly  used  by  amateurs  at  the  present  time,  while  the  two  following  lessons  will 

treat  on  the  more  complicated  commercial  transmitters,  as  well  as  the  latest  advances 

made  in  this  direction. 

The  student  has  learned  that  the  simplest  set  for  producing  electro-magnetic 
waves  consists  of  a  spark  coil  with  the  Hertz  Oscillator,  and  connections  made 
to  an  aerial  and  a  ground  wire.  This  is  the  type  of  transmitter  originally  used  by 
Marconi  in  his  earlier  commercial  apparatus.  In  consequence,  the  simplest  apparatus 
at  the  command  of  the  amateur  wireless  student,  will  be  based  on  this  principle 
and  is  illustrated  in  fig.  1.  Here,  the  coil  is  shown  with  two  large  binding  posts  into 
which  two  rods  can  slide  so  as  to  vary  the  gap  between  the  two  brass  balls.  A 
telegraph  key  has  been  interposed  at  K,  so  that  the  circuit  may  be  made  and  broken 
to  form  the  dots  and  dashes  for  the  forming  of  the  code  signals.  At  B,  a  number 
of  cells  have  been  arranged  to  furnish  current  to  the  spark  coil.  The  aerial  and 
ground  wires  are  connected  to  both  rods  of  the  spark  balls. 


Fig.  1. 

The  brass  balls  from  the  spark  gap  have  been  abandoned  at  the  present  time 
for  metal  rods.  These  brass  balls  are  satisfactory  where  a  small  spark  coil  is 
employed,  but  when  using  greater  current  in  the  spark  gap,  they  prove  inadequate 
to  serve  the  purpose.  The  brass  becomes  heavily  oxidized  where  the  spark  forms, 
and  thus  presents  a  poor  surface  and  consequently  a  rough  spark  after  short  use. 
Many  metals  have  been  tried,  and  zinc  has  been  found  to  be  the  most  practical. 
In  sets  of  small  power,  two  zinc  rods  fitted  with  insulated  handles  are  used  for 
a  spark  gap  and  illustrated  in  fig.  2.  The  spark  gap  should  be  adjusted  so  that  the 
spark  is  smooth  and  fills  the  entire  gap  with  a  solid  discharge.  By  drawing 
the  gap  too  large,  the  discharge  becomes  broken  up  and  each  spark  weak  and  stringy; 
the  oscillations  produced  in  the  aerial  being  likewise  broken  up  and  not  readable 
at  the  receiving  end.  With  the  type  of  set  mentioned  previously  and  illustrated 
in  fig.  1,  the  spark  should  be  no  longer  than  l/8th  of  an  inch,  using  a  1-inch  coil 
with  a  suitable  aerial,  and  if  a  2-inch  coil  is  employed,  this  length  may  perhaps  be 
as  great  as  3/16ths  or  1/4  of  an  inch.  The  main  object  to  be  kept  in  mind,  is  that  the 
spark  should  be  smooth,  and  jump  between  every  portion  of  the  surfaces,  instead 
of  from  one  single  point. 

Spark  coils  are  rated  according  to  the  length  of  the  spark  they  will  produce 
between  needle  points  when  used  with  the  proper  primary  current.  Thus,  if  a  coil 
is  rated  as  a  2-inch  coil,  this  signifies  that  this  coil  when  connected  to  the  required 
number  of  batteries  will  cause  a  spark  to  jump  between  needle  points  spaced  2 
inches  apart  or  less.  Coils  made  by  reputable  firms  are  always  under-rated,  so 
that  a  2-inch  coil  may  be  found  to  give  perhaps  a  2  1/2-inch  or  a  3-inch  spark 
between  needle  points.  The  following  table  denotes  the  number  of  cells  of  different 
types  to  employ  with  standard  spark  coils: 

Convrisrht  1912  by  E.   I.  Co. 


34 


WIRELESS  COURSE— LESSON  NO.  5 


"  use  2  storage  cells  or  3  primary  cells,  or    3  dry  cells. 


or  4 
or  5 
or  6 
or  7 

or  8 


or  4 
or  6 
or  7 
or  12 
or  24 


In   multiple. 


Fig.  3  represents  one  of  the  most  practical  type  of  spark  coils  placed  on  the 
market  to  meet  the  needs  of  the  amateur  and  sold  at  a  moderate  price.  It  is 
known  as  the  "Bull-Dog"  type  of  spark  coil,  the  insulation  and  other  construction 
features  being  of  the  very  best.  The  vibrator  on  this  coil,  as  in  many  other  standard 
spark  coils,  consists  of  a  steel  and  phosphor-bronze  strip  firmly  held  on  a  brass 
block  to  the  side  of  the  coil.  The  iron  core  of  the  coil  is  just  in  back  of  this  spring 
which  is  known  as  the  "vibrator  spring,"  and  as  previously  described  in  a  past 
lesson,  the  core  attracts  the  vibrator,  but  on  being  attracted,  this  vibrator  breaks 
the  contact  between  two  platinum  points,  one  being  on  the  spring  itself,  while 
the  other  is  at  the  end  of  a  thumb-screw  mounted  on  the  brass  bridge  in  front 
of  the  vibrator.  The  adjustment  of  the  coil's  vibrator  is  highly  important,  since 
the  size  of  the  spark  and  its  smoothness  depend  to  a  large  degree  on  the  action  of 
the  vibrator.  The  vibrator  should  be  adjusted  by  connecting  the  batteries  and  then 
turning  the  thumb-screw  in  tfne  direction  or  another  until  the  spark  is  at  its  best. 
If  the  spark,  ceases,  the  cause  is  that  the  vibrator  screw  has  been  turned  too 
far  in  either  direction.  The  vibrator  spring  should  be  sufficiently  free  from  the 
contact  screw  to  be  able  to  move  readily,  yet  the  speed  should  be  quite,  high  and 
steady. 


I. 

r 


Fig.  3 


In  the  first  set  described  in  this  lesson,  the  system  is  known  as  the  "plain  aerial 
system,"  since  no  closed  oscillating  circuit  is  employed,  but  the  aerial  and  ground 
act  as  direct  capacities  to  the  spark  gap.  Open  circuit  transmitters,  as  in  open 
circuit  receivers,  are  not  efficient,  and  hence  little  used.  The  reason  is  best  explained 
by  quoting  the  following  extract  from  the  excellent  work  of  the  authority,  George 
W.  Pierce,  entitled  "Principles  of  Wireless  Telegraphy." 


S.G. 


COIL- 


Fig.  5 


"A  closed  condenser  circuit  is  not  a  good  radiator  of  electrical  energy,  hence 
an  antenna  is  employed  for  the  purpose  of  radiating  the  energy.  But  on  account 
of  the  comparatively  small  capacity  of  the  antenna,  we  cannot  easily  apply  large 
amounts  of  power  directly  tP  the  antenna  so  as  to  get  the  necessary  high  potential. 


WIRELESS  COURSE— LESSON  NO.  5 


35 


Now,  the  use  of  a  long  spark  gap  carries  with  it  disadvantages;  it  does  not  produce 
good  oscillations. 

"To  avoid  this  disadvantage,  the  high  potential  in  the  antenna  is  obtained,  not 
by  the  use  of  a  long  spark  gap,  but  by  the  inductive  action  of  a  discharge  occurring 
in  a  condenser  circuit  connected  with  the  antenna  and  put  into  resonant  relation 
with  it,  (as  shown  in  figs.  4  and  5).  The  larger  amount  of  power  in  the  condenser 
circuit  is  attained  by  the  largeness  of  the  capacity,  instead  of  by  the  length  of  the 
spark  gap.  By  the  use  of  a  suitably  large  capacity  in  the  condenser  circuit,  we 
can  obtain  tremendous  current  in  the  circuit,  which  will  induce  very  large  potential 
in  the  antenna,  if  the  antenna  is  in  resonance  with  the  condenser  circuit.  Thus 
we  get  a  large  amount  of  radiation." 


Fig.  6 


Ficr.  7 


The  reader  will  accordingly  note  from  the  foregoing  explanation,  that,  as  in 
the  instance  of  the  receiving  sets  described  in  the  previous  lesson,  it  is  necessary  to 
have  a  closed  circuit  transmitting  set  to  obtain  the  maximum  results.  If  a  plain 
aerial  connection  is  used,  the  spark  gap  must  by  necessity,  be  of  a  great  length, 
therefore  producing  a  great  difference  of  potential  between  the  aerial  and  the  earth. 
This  is  a  very  undesirable  feature;  on  shipboard  or  where  dampness  exists,  in 
particular;  and  everywhere  in  general,  since  such  an  aerial  and  apparatus  cannot 
be  insulated  without  great  difficulty.  For  small  sets,  intended  to  communicate 
from  a  fraction  of  a  mile  to  about  15  miles,  this  system  may  be  used,  but  the  closed 
circuit  transmitter  must  be  resorted  to  for  greater  distances. 

In  order  to  change  the  plain  aerial  set  into  a  closed  circuit  transmitter,  a  few 
turns  of  heavy  wire  in  the  form  of  a  helix,  and  interposed  between  the  aerial  and 
ground  connections,  are  used.  A  condenser  must  also  be  added.  Fig.  4  illustrates 
the  connections  used  for  the  closed  oscillating  type  of  transmitter.  (C-Condenser, 
H-Helix.) 


Fig.  8  Fig.  9 

The  few  turns  of  wire  are  mounted  on  a  suitable  framework,  and  clips  or  other 
contacts  are  used  to  vary  the  number  of  turns  across  which  the  condenser  and 
spark  gap  are  placed.  Fig.  6  illustrates  a  very  popular  type  which  may  be  used 
for  coils  up  to  6  inches  with  ease,  and  consists  of  a  number  of  turns  of  brass  strip 
wound  spirally  on  an  insulated  drum.  The  sliding  contact  mounted  on  the  brass 
rod  enables  the  turns  to  be  varied  in  the  oscillation  circuit,  while  the  aerial  and 
ground  wires  are  connected  to  the  two  end  binding  posts  of  the  entire  turns.  Thus 
in  this  type  of  helix  the  aerial  turns  remain  fixed,  but  the  oscillation  circuit  turns 


36 


WIRELESS  COURSE— LESSON  NO.  5 


are  variable  so  as  to  obtain  the  resonance  effect  between  the  two  circuits.  Fig. 
7  illustrates  another  type  which  is  very  popular  with  the  amateurs  using  small 
coils  of  from  a  fraction  of  an  inch  to  2  inches.  Again,  in  this  type,  the  turns  are 
of  flat  brass  strip  and  held  in  place  by  grooves  and  notches  in  the  wooden  b,ack 
board.  The  turns  are  wound  concentrically,  so  that  the  entire  helix  is  flat  and 
occupies  the  minimum  of  space.  Two  small  clips  attached  to  flexible  cords  enable 
the  oscillation  circuit  to  be  varied  as  well  as  the  aerial  circuit,  shown  in  a  diagram 
which  will  be  given  later.  By  varying  both  the  aerial  and  closed  condenser  cir- 
cuits, the  maximum  resonance  effects  are  obtained.  This  type  of  flat  helix  is  com- 
monly known  as  the  "pan-cake"  type.  Fig.  8  represents  the  universally  adopted 
standard  type,  used  in  commercial  practice  as  well  as  with  the  better  equipped 
amateur  stations.  The  turns  of  wire  are  passed  through  holes  in  the  wooden 
uprights,  while  special  clips  enable  connections  to  be  made  at  any  part  of  the 
turns.  A  small  lamp  has  also  been  added  at  the  -upper  end  of  the  helix  so  that 
the  degree  of  resonance  between  the  two  circuits  may  be  gauged  by  the  brilliancy 
of  the  light.  This  lamp  is  commonly  known  as  the  "pilot  lamp." 

As  for  the  condenser,  any  type  employing  glass  for  the  dielectric  will  prove 
satisfactory,  providing  that  it  is  of  the  correct  capacity,  and  will  not  break  down. 
A  very  neat  arrangement  for  small  sets  employing  coils  not  larger  than  2  inches, 
can  be  seen  in  fig.  9.  A  number  of  tubular  leyden  jars  are  noticed  mounted  in 
a  special  wooden  framework.  The  leyden  jars  are  held  in  place  by  spring  devices, 
so  that  they  can  be  instantly  slipped  in  or  out  of  the  rack,  thus  varying  the  capacity 
until  the  .proper  amount  of  condenser  is  obtained.  The  capacity  should  be  adjusted 
until  the  spark  fills  the  gap  with  a  solid  crashing  flame,  but  if  too  much  capacity 
is  used,  there  will  be  little  if  any  spark,  since  the  coil  will  have  to  take  a  much 
longer  time  to  charge  the  condenser  to  a  point  where  it  can  break  down  and 
discharge  over  the  gap.  This  condenser  is  patented  by  H.  Gernsback. 


Fig.  10 


Fig.  11 


Fig.  12 


If  larger  coils  than  2-inch  spark  length  are  employed,  it  is  necessary  to  use 
a  glass  plate  or  leyden  jar  condenser  of  great  dimensions.  A  glass  plate  condenser 
consists  of  many  plates  of  glass  coated  on  both  sides  with  metal  sheets.  The 
usual  type  employs  heavy  tinfoil,  which  is  fastened  securely  on  the  glass  by  thinned 
orange  shellac,  banana  oil,  or  other  adhesive.  The  entire  plates  are  well  shellacked 
around  the  edges  of  the  tinfoil  coating,  so  that  the  "brush  discharges"  are  reduced 
to  a  minimum.  Fig.  10  illustrates  the  arrangement  of  the  metal  coating  on  the 
glass  plate,  and  it  will  be  noticed  that  the  tin  foil  used  in  this  instance  is  cut  so 
that  a  portion  or  "tongue"  protrudes  past  the  glass  plate.  This  tongue  is  to  make 
connections  with  the  other  apparatus,  and  all  the  tongues  on  ooe  side  are  con- 
nected together,  thus  forming  a  parallel  condenser.  Both  sides  of  this  glass  sheet 
are  alike,  and  the  tongue  from  the  tin  foil  coating  on  the  reverse  side  will  be 
noticed  protruding  past  the  glass.  The  plates  are  mounted  on  a  small  wooden 
framework  arranged  with  suitable  notches  or  blocks  in  order  to  space  the  plates 
at  least  an  inch  apart.  The  wiring  connections  are  shown  in  fig.  11.  Another 
method,  which  is  also  used  to  a  great  extent,  differs  from  the  foregoing  by  the 
placing  of  the  metal  coatings  between  each  two  pieces  of  glass,  so  that  alternately 
there  will  be  a  metal  surface,  then  glass,  then  metal,  then  glass,  then  metal,  etc. 
This  enables  the  plates  to  be  placed  touching  each  other,  thus  making  the  con- 
denser very  compact.  The  one  great  disadvantage,  however,  is  in  the  fact  that  if  one 
plate  should  break  down,  it  will  necessitate  the  entire  deranging  of  the  plates  to 
locate  and  remove  the  affected  plate,  whereas  in  the  previous  system,  where  the 
plates  were  separated,  the  broken  plate  can  be  immediately  found  and  removed 
without  disturbing  the  other  plates.  However,  if  the  condenser  is  properly  made, 
breakdowns  are  rare.  When  the  plates  have  been  completely  coated  and  placed 
together,  they  are  bound  with  heavy  cord,  and  then  placed  in  a  neat  wooden  case. 
Molten  paraffine  is  then  poured  into  the  box,  and  upon  cooling,  it  hardens,  thus 
forming  a  solid  insulating  mass  around  the  condenser.  Fig.  12  illustrates  how 
the  plates  should  be  connected  before  the  condenser  is .  placed  in  the  box.  In 
this  type  of  condenser,  thin  aluminum  or  copper  sheeting  are  highly  recommended, 
for  the  coating  is  naturally  held  in  place  by  the  tight  binding  of  the  plates  with 
the  cord,  and  no  adhesive  need  be  used. 

The  following  table  gives  the  proper  dimensions  of  glass  plate  condensers  for 
standard  spark  coils: 


WIRELESS  COURSE— LESSON  NO.  5 


37 


•2  >> 

f'S 

f    •— 

Iflsa 

•  —  '  —  ••—<  ^  ,"" 

a 

Si 

|J 

«*-<  '3  -ft 

1*  s 

o  ~ 

^  Ai       4)  •— 

O  T-" 

•$H  "^ 

.J3.S  S 

®  c6  O 

55 

^  £  '?  -" 

<a 

H'^ 

c^  Ow-3 

|5« 

Oco 

' 

X 

18 

12  in.  x  14  in. 

^  in.  x  10  in. 

.0048 

/^ 

34 

12  in.  x  14  in. 

Sin.  x  10  in. 

.0095 

1 

40 

Iti  in.  x  19  in. 

10  in.  x  13  in. 

.019 

2 

80 

1  6  in.  x  19  in. 

10  in.  x  13  in. 

.037 

^ 

120 

16  in.  x  19  in. 

10  in.  x  13  in. 

.05fi 

4 

160 

1  6  in.  x  19  in. 

10  in.  x  13  in. 

.074 

5 

200 

16  in.  x  19  in. 

10  in.  x  13  in. 

J93 

"Electro"  High  Tension  Condenser. 


When  condensers  are  used  on  coils  which  are  slightly  too  large  for  the  capacity 
of  the  condenser,  a  series  of  small  purple  sparks  giving  as  a  whole  the  appearance 
of  a  purple  fringe  of  light,  will  appear  around  the  edges  of  the  tin  or  metal  foil. 
This  is  known  as  the  "brush"  or  "brush  discharge."  It  is  then  that  a  peculiar 
and  strong  odor  is  noticed,  and  which  is  known  as  ozone,  this  gas  being  formed 
by  the  silent  discharges.  Brush  discharges  indicate  a  loss  of  power,  and  should  be 
reduced  to  a  minimum.  When  there  is  too  much  brush  discharge,  more  condenser 
should  be  added,  or  the  edges  of  the  foil  and  uncovered  glass  margin  should  be 
shellacked  or  coated  with  black  asphaltum  paint,  if  it  has  not  been  thus  treated 
already.  A  margin  of  at  least  1  inch  should  always  be  left  between  the  foil  and 
the  edge  of  the  glass.  If  the  coil  is  too  powerful  entirely  for  the  condenser, 
the  glass  often  is  pierced  by  the  electric  discharges,  and  shatters  completely.  It  is 
for  this  reason  that  the  spark  gap  in  the  set  should  never  be  left  beyond  the  point 
where  the  discharge  from  the  condenser  can  pass  without  difficulty  while  in  the 
circuit. 

Fig.  13  illustrates  the  exact  connections  used,  and  it  will  be  noticed  that  the 
condenser  is  placed  across  the  spark  coil,  while  the  spark  gap  is  placed  in  series 
with  the  few  turns  in  the  helix.  The  two  clips  are  so  arranged  as  to  vary  either  the 
aerial  circuit  or  the  oscillating  circuit,  in  order  to  obtain  the  maximum  resonance. 
In  a  later  lesson,  the  tuning  of  the  two  circuits  to  secure  resonance  is  described 
at  length  as  well  as  the  special  wave  meters  by  which  the  wave-length  of  the  trans- 
mitter can  be  determined. 


As  yet,  only  sets  employing  batteries  to  operate  the  coils  have  been  discussed. 
However,  in  order  to  cover  greater  distances,  it  is  necessary  to  resort  to  greater 
power  and  larger  coils,  so  that  batteries  must  be  abandoried  in  favor  of  current 
from  power  circuits.  In  using  open  core  transformers  or  spark  coils  of  small 
dimensions,  a  special  interrupter  must  be  employed  if  either  direct  or  alternating 
current  is  being  used.  This  corresponds  to  the  vibrator  attached  to  the  smaller 
spark  coil,  and  serves  the  same  purpose.  There  are  various  forms  of  these  inter- 
rupters, the  most  popular  types  being:  the  electrolytic;  the  magnetic;  and  the 
motor  driven  interrupter. 

The  electrolytic  interrupter  operates  on  the  principle  that  when  electric  current 
passes  through  acidulated  water,  gases  are  formed  at  the  electrodes.  These  gases 
are  poor  conductors,  the  current  is  practically  stopped,  but  in  so  doing,  the  heavy 
and  high  voltage  induced  current  in  the  primary  winding  of  the  induction  coil  rushes 
to  the  point  where  the  gas  has  been  formed  and  breaks  down  the  insulation  of 
the  bubble  of  gas,  thus  permitting  the  current  to  again  pass  and  the  foregoing 
action  to  be  repeated.  Of  course,  the  reader  must  appreciate  that  this  takes  place 
almost  instantaneously,  the  interruptions  being  between  100  and  2,000  per  second, 
depending  on  the  inductance  of  the  circuit  and  the  voltage  used.  Electrolytic  inter- 


WIRELESS  COURSE— LESSON  NO.  5 

rupters  will  not  operate  on  lower  voltages  than  40  volts,  and  operate  either  on 
direct  or  alternating  current,  but  with  greater  efficiency  on  the  former.  The  positive 
pole  of  the  direct  current  power  supply,  if  direct  current  is  used,  should  always 
be  connected  to  the  electrode  where  the  gas  must  form,  in  the  Wehnelt  type  being 
the  platinum  or  metal  rod  protruding  through  the  insulating  tube,  and_in  the  Cald- 
well  type  this  being  the  rod  contained  in  the  inner  jar. 

The  .electrolytic   interrupter   of   the   most   successful   type   is    the   Wehnelt   inter- 
rupter,  which   consists   of   a   metal    (usually  platinum,   which   gives    the   best   results) 


%  HOLE  THREADED 
TO  FIT    F 


HARD   RUBBLR 

OK  FIBRE.   TUBE 
.F     -,r 


SPARK 
PLUG   PORCELAIN 

(Courtesy  "Modern  Electrics.") 

rod  protruding  through  a  porcelain  or  glass  tube,  which  is  immersed  in  the  acidulated 
water.  A  large  lead  rod  or  plate  is  used  as  the  other  electrode  for  the  passage  of 
the  current  through  the  liquid.  The  current  flows  from  the  metal  point  to  the 
lead  plate.  The  solution  consists  of  4  parts  of  pure  water  to  1  part  of  sulphuric 
acid.  The  Wehnelt  interrupter  illustrated  in  fig.  14  is  an  excellent  and  simple  type 
which  may  be  readily  made  by  the  reader.  The  positive  pole  of  the  direct  current 
supply  is  connected  to  the  brass  part  C,  while  the  negative  pole  is  attached  to  the 
lead  rod.  L  is  a  fibre  handle;  E  is  a  threaded  rod,  which  is  constructed  to  fit  the 
threaded  handle,  but  slotted  so  as  to  engage  the  pin  F  and  prevent  it  from  turning; 
H  is  a  copper  rod,  though  platinum  is  far  more  suitable;  D  is  a  brass  tube  as  shown; 
M  is  the  overflow  hole  in  the  fibre  tube,  into  the  lower  end  of  which  a  portion 
of  an  old  spark  plug  porcelain  part  has  been  driven;  finally,  C  is  a  small  brass 
block  as  shown.  This  is  the  adjustable  type  of  Wehnelt  interrupter,  since  the  fibre 
handle  can  be  operated  to  allow  more  or  less  surface  to  be  exposed  to  the  acidulated 
water. 

Another  type  of  electrolytic  interrupter  is  represented  at  C  in  fig.  15.  In  this 
instance,  a  platinum  wire,  (about  No.  6  B  &  S  will  give  excellent  results  for  coils 
up  to  6  inches)  has  been  placed  in  the  end  of  a  glass  tube  while  the  glass  was  in 
a  molten  condition,  thus  making  a  perfect  joint  at  the  end  where  the  platinum  is 


Fig.  15  Fig.  16 

exposed.  Mercury  is  placed  in  the  bottom  of  the  tube  so  that  it  touches  the  mer- 
cury and  enables  contact  to  be  made  with  a  wire  which  is  inserted  through  the  top 
of  the  tube  and  dips  into  the  mercury.  This  is  a  fixed  type  of  Wehnelt  interrupter, 
since  the  point  is  non-adjustable. 


WIRELESS  COURSE— LESSON  NO.  5 


39 


Still  another  type,  known  as  the  Caldwell  type,  uses  two  electrodes  which  are 
separated  by  one  of  these  being  placed  in  a  jar  which  has  a  small  hole,  and  operates 
upon  the  same  principle  as  the  Wehnelt,  the  gas  in  this  instance  forming  at  the 
opening  of  the  inner  jar.  Though  this  type,  illustrated  in  fig.  15,  is  very  simple  to 
construct,  it  is  not  as  popular  as  the  Wehnelt  type. 

A  great  advancement  in  electrolytic  interrupters  was  marked  by  the  introduc- 
tion of  a  perfected  interrupter,  illustrated  in  fig.  16.  and  known  as  the  Gernsback  type. 
Notwithstanding  the  fact  that  it  is  sold  at  a  popular  price,  within  the  reach  of  all 
experimenters,  it  will  give  results  which  can  favorably  compare  with  the  more 
expensive  types,  in  many  instances  even  surpassing  these  expensive  interrupters  in 
efficiency.  The  Gernsback  interrupter  is  composed  essentially  of  a  porcelain  cover 
and  a  detachable  tube  into  which  a  metal  rod  passes  and  fits  into  a  small  aperture 
in  the  bottom  of  this  tube.  A  small  sliding  weight  fits  over  the  top  of  the  rod  and 
serves  the  combined  purposes  of  conveying  the  current  to  the  rod,  and  to  feed 
the  rod  downwards  into  the  small  hole  as  it  wears  down.  If  desired  the  rod  may  be 
slightly  lifted  into  the  tube  and  held  in  place  by  the  adjustment  screw  on  the 
aluminum  bridge,  and  will  then  operate  as  a  Caldwell  interrupter.  A  lead  strip 
dips  into  the  regular  solution,  which  has  already  been  mentioned,  and  from  time 
to  time  may  be  cleaned  with  a  knife  and  sand-paper  to  remove  the  brown  or  black 
coating  which  forms  on  it.  A  large  tablespoonful  of  household  ammonia  added 
to  the  solution  will  also  add  to  the  results.  This  interrupter  may  be  used  on  all 
induction  coils  from  J^-inch  to  12-inch,  no  resistance  being  necessary  with  circuits 
of  about  110  volts.  If  ordinary  spark  coils  are  being  used,  the  vibrator  contact 
screw  should  be  turned  so  that  it  is  firmly  pressed  on  the  vibrator  spring  to  prevent 
it  from  moving.  Better  still,  a  small  piece  of  wire  can  be  placed  between  the  brass 
bridge  and  the  brass  block  holding  the  vibrator  spring. 


Fig.  19 


Fig.  17 
(Courtesy  "Modern  Electrics.") 

The  magnetic  type  of  interrupter  (fig.  17)  operates  on  the  same  principle  as  the 
vibrator  on  the  spark  coils.  It  consists  of  a  pair  of  electro-magnets  which  attract  an 
iron  armature  which  carries  the  contacts.  Against  these  contacts  are  others,  located 


110 
VOLTS 


COIL 


Fig.  18 


on  posts  and  adjustable  by  suitable  screws.  Many  adjustments  are  used  so  that 
the  mechanical  features  may  be  varied  until  the  best  results  are  obtained.  The 
interruptions  with  this  device  are  very  slow,  producing  low  frequency  sparks,  which 


40 


WIRELESS  COURSE— LESSON  NO.  5 


are  not  desirable  in  all  instances.  In  consequence  of  this  low  speed,  it  can  only  be 
used  in  connection  with  a  few  storage  batteries  or  on  110  volts  if  a  suitable  resist- 
ance is  inserted  to  reduce  the  voltage. 

The  motor-driven  interrupter  consists  of  a  small  power  motor  driving  rotating 
contacts  which  dip  in  mercury.  There  are  many  types,  varying  widely  in  mechanical 
details,  the  most  successful  type  being  that  in  which  the  motor  operates  a  small 
turbine  pump  which  throws  a  steady  stream  of  mercury  against  a  rapidly  revolving 
toothed  wheel,  consequently  making  and  breaking  the  circuit.  The  great  advantage 
in  these  motor-driven  interrupters  lies  in  the  fact  that  the  interruptions  may  readily 
be  changed  by  merely  varying  the  speed  of  the  motor.  Owing  to  the  high  speed 
of  the  interruptions,  it  may  be  used  directly  on  110  volts  with  coils  of  6  inches  or 
larger,  but  with  smaller  coils  it  is  adviseable  to  employ  a  resistance  in  series  with  the 
current  supply. 

Fig.  18  represents  a  transmitting  set  arranged  for  using  110  volts  with  an  electro- 
lytic interrupter,  but  any  other  type  of  interrupter  as  described  in  the  foregoing  may 
be  substituted  if  the  resistance  is  also  inserted  in  the  circuit.  This  represents  the 
best  possible  installation  for  an  amateur  station  employing  a  spark  coil  or  open 
core  transformer. 


SUDDS 


Fig.  20 


Fig.  21 


As  the  student  has  learned  in  the  study  of  the  principles  of  electricity,  he  will 
remember  that  open  core  transformers  are  not  to  be  compared  with  the  efficiency 
of  closed  core  transformers.  If  the  amateur  wishes  to  have  a  still  better  station, 
and  one  capable  of  covering  distances  up  to  100  and  even  200  miles,  as  against  25 
miles,  which  could  be  covered  with  the  open  core  transformers  and  spark  coils, 
he  must  resort  to  a  closed  core  transformer  of  high  power,  and  alternating  cur- 
rent. Fig.  19  illustrates  a  closed  core  transformer. 

With  the  use  of  a  transformer,  the  entire  accessory  apparatus  must  be  of  heavier 
and  more  substantial  nature  than  when  using  ordinary  small  spark  coils.  Fig.  20 
illustrates  the  extra  large  spark  gap  employed,  which  has  two  parallel  surfaces 
of  zinc,  which  may  be  separated  further  by  turning  the  hard  rubber  knob.  The  gap 
is  mounted  on  rubber  pillars  to  increase  the  insulation.  When  using  spark  gaps 
on  large  transformers,  they  are  sometimes  placed  in  boxes  so  as  to  reduce  the  noise 
caused  by  the  spark.  Then  the  gap  is  known  as  "muffled."  Fig.  21  illustrates  the 
heavy  key  equipped  with  special  platinum  contacts  of  large  dimensions  to  handle 
the  heavier  current.  These  contacts  are  embedded  in  mica,  which  can  withstand  the 
intense  heat.  A  condenser  composed  of  many  sheets  of  tin  foil  and  paraffined  paper 
is  often  placed  in  parallel  across  these  contact  points  to  reduce  the  excessive  spark- 
ing if  found  necessary.  The  helix  should  likewise  be  of  heavy  construction,  and 
whereas  No.  8  wire  was  suitable  for  the  smaller  coils,  in.  this  instance  it  must  be 
much  larger  in  proportion.  For  a  l/±  K.  W.  transformer,  the  wire  should  be  no 
smaller  than  No.  6,  for  y3  K.  W.  no  smaller  than  No.  4,  and  for  1  K.  W.  no  smaller 
than  No.  0.  The  larger  transformers  should  be  equipped  with  helixes  of  still  larger 
wire. 

In  the  descriptions  of  complete  stations,  the  student  will  learn  that  special 
switches  are  used  for  connecting  the  aerial  and  ground  either  to  the  sending  or 
receiving  sets  as  well  as  to  disconnect  the  power  circuit  from  the  transformer. 
This  is  known  as  an  antenna  or  aerial  switch. 

(To  be  continued  next  lesson) 


WIRELESS  COURSE— LESSON  NO.  6 


41 


Lesson  Number  Six. 


TRANSMITTING  SETS  (Continued). 

E   student  has  learned   from   the  previous  lesson  that  a   special   switch  known 
as  the  Aerial  Switch,  is-  employed  for  connecting  the  transmitter  or  receiver  re- 
spectively  to  the  aerial  and  ground,  for  the  purpose  of  communicating  to  and 
from  a  station.  • 

The  simplest  type  of  aerial  switch  is  shown  in  fig.  1,  and  is  an  ordinary  double 
pole,  double  throw,  porcelain  base  switch.  The  base  may  be  of  other  material,  but 
either  hard  rubber  or  porcelain  serve  the  purpose  best.  Instead  of  running  the  connec- 
tions directly  to  the  ground  and  aerial,  as  illustrated  in  the  diagrams  heretofore,  the 
leads  from  the  transmitter  are  connected  to  the  two  jaw  posts  on  one  end,  and  the  leads 
from  the  receiving  set  are  connected  to  the  two  jaw  posts  on  the  opposite  end,  while 
the  aerial  and  ground  connections  are  made  at.  the  center  hinge  posts.  Fig.  2 
illustrate*  the  connections  as  described. 


Fig.  1. 


TO  TRANSMITTER 

., e 


TO  RECEIVER 


Fig.  2. 


Though  this  simple  switch  will  serve  the  purpose  for  small  sets  operating 
with  coils  of  smaller"  sizes  than  2  inches,  with  larger  coils  and  transformers,  more 
elaborate  and  superior  switches  must  be  used.  The  great  disadvantage  of  this 
simple  switch,  even  when  used  on  small  power,  is  the  fact  that  the  movement  of  the 
.blades  when  either  set  is  to  be  connected,  is  great  and  requires  more  effort  than 
if  the  throw  was  less  distanced,  which  would  be  possible  by  various  methods,  as  will 
be  presently  discussed.  Instead  of  causing  the  complete  throw  to  swing  through  an 
angle  of  180  degrees,  the  blades  might  so  be  arranged  that  only  90  degrees  or  even 
45  degrees  completes  the  throw,  thus  saving  time  and  effort.  Another  marked 
disadvantage  lies  in  the  fact  that  -the  transmitting  primary  current  is  still  connected 
to  the  key  and  coil  even  when  the  switch  has  been  thrown  to  the  receiving  set. 
Should  the  key  be  pressed  accidentally  while  the  receiver  is  connected  to  the  aerial 
and  ground,  the  sensitive  apparatus  of  the  receiving  set  will  temporarily  lose  its 
adjustment  and  ability  to  receive  messages.  Dangerous  shocks  to  the  operator 
might  also  result  from  the  lack  of  disconnecting  the  primary  current.  It  is  there- 
fore evident  that  this  aerial  switch  must  also  include  another  contact  to  disconnect 
the  primary  circuit  of  the  transmitter  when  same  is  disconnected  from  the  aerial 
circuit. 


Fig.  3. 


A  very  simple  yet  effective  aerial  switch  in  which  both  these  foregoing  disad- 
vantages have  been  eliminated,  is  the  "Electro"  Aerial  Switch  illustrated  in  fig. 
3.  This  switch  has  three  blades,  and  on  one  end  there  are  thfee  jaw  posts,  but  on  the 
opposite  end  there  are  but  two  jaw  posts  to  engage  the  two  outside  blades  of  the 
switch.  The  center  blade  is  connected  in  serie%  with  the  primary  of  the  trans- 

Convriirlit   1!»1->   liv   R     I     f\i 


42 


WIRELESS  COURSE— LESSON  NO.  6 


mitter,  as  illustrated  in  fig.  4,  while  the '  receiving  and  transmitting  leads  are  con- 
nected to  their  respective  jaw  posts.  Aside  from  the  additional  blade,  the  switch 
is  the  same  relative  to  the  wiring  as  in  the  simple  switch  previously  described. 
However,  another  improvement  is  found  in  the  extended  and  bent  blades,  which 
enable  the  switch  to  be  thrown  from  one  set  of  jaw  posts  to  the  other  set  with  the 
minimum  movement  and  effort. 


TO 

RECEIVING 
SET 


In  commercial  stations  the  aerial  switches  are  far  more  complicated,  and  operate 
a  number  of  circuits  by  a  simple  throw.  These  switches  are  made  in  a  variety  of 
forms,  in  some  the  rotating  blades  are  mounted  on  an  insulated  drum,  while  in  others 
the  contacts  are  mounted  on  a  long  arm.  Every  system  has  its  particular  design 
of  aerial  switch,  and  inasmuch  as  the  operation  is  identical  in  each  instance,  further 
description  is  useless.  One  important  point  that  the  student  will  discover  is  this; 
that  in  order  to  make  a  number  of  connections  with  a  moderately  simple  switch, 
only  the  aerial  can  be  disconnected  from  the  two  sets,  so  that  the  ground  is  per- 
manently connected  to  both  the  transmitting  and  receiving  instruments.  This  necessi- 
tates the  use  of  a  small  spark  gap  in  the  aerial  for  the  transmitter;  this  gap  being 
known  as  the  "Anchor  Gap."  This  usually  consists  of  two  pointed  brass  rods  spaced 
a  fraction  of  an  inch  apart.  In  other  types  three  brass  rods  are  used,  where  a 
special  type  of  aerial  known  as  the  "loop"  aerial  is  employed.  In  fig.  5  will  be 


Fig.  5 


seen  a  diagram  illustrating  the  reason  for  employing  an  anchor  gap  in  commercial 
installations.  It  will  be  noted  that  the  anchor  gap  enables' the  transmitter  to  be 
continuously  connected  to  the  aerial  and  ground,  inasmuch  as  the  high  voltage 
current  from  the  transmitter  easily  travels  across  the  small  gap.  The  gap  is  there- 
fore employed  so  that  the  current  from  the  aerial  to  the  receiving  set  will  not  be 
grounded  through  the  transmitting  helix.  A  hard  rubber  handle  is  illustrated  for 
an  aerial  switch,  on  one  end  having  the  contact  4  connected  to  the  aerial  lead  above 
the  aerial  gap,  and  making  connections  with  the  receiving  apparatus  when  pushed 


WIRELESS  COURSE— LESSON  NO.  6  43 

down  and  touching  contact  2.  In  so  doing,  the  contacts  at  1,  which  are  connected 
in  series  with  the  primary  circuit  of  the  transmitting  apparatus,  are  no  longer  bridged 
by  the  metal  extension  3,  so  that  the  receiving  set  is  connected  to  the  aerial  with 
no  danger  of  current  from  the  transmitter  effecting  it.  The  rubber  handle  is  then 
thrown  up  when  the  operator  desires  to  send,  and  in  so  doing,  the  metal  part  3 
bridges  tne  two  contacts  1,  closing  the.  primary  circuit  of  the  transmitter,  and  on 
pressing  the  key  the  transmitter  operates.  In  throwing  up  the  switch  it  also  dis- 
connects the  receiver  at  2,  thus  avoiding  all  danger.  By  mounting  additional  contact 
surfaces  on  the  rubber  arm,  any  circuits  in  the  receiving  set  may  be  opened  or 
closed.  It  will  thus  be  seen  that  the  purpos-e  of  the  anchor  gap  is  to  simplify 
the  switching  from  transmitter  to  receiver.  An  anchor  gap  consumes  considerable 
energy,  reducing  the  range.  In  sets  of  1  K.  W.  and  larger,  this  loss  is  negligible, 
but  in  smaller  sets  an  anchor  gap  is  discouraged,  and  it  is  better  to  use  more  com- 
plicated switches  and  avoid  the  loss  of  power.  All  commercial  systems  of  any 
importance  have  adopted  the  anchor  gap,  and  various  types  of  simple  switches  for 
this  operation. 

Commercial  installations  of  reasonable  size  do  not  employ  spark  coils  as  a  rule, 
though  a  few  exceptions  will  be  found  that  do.  Most  stations  of  reasonable  size 
and  range  use  an  open  or  closed  core  transformer  operated  on  alternating  current. 
Another  complication  soon  arises  that  renders  the  commercial  station  a  veritable 
power  house  as  compared  to  the  modest  amateur  station.  In  order  to  obtain  the 
alternating  current  for  the  transformer,  a  special  motor-generator  set  is  employed, 
with  a  direct  current  motor  of  suitable  voltage  driving  a  direct-connected  generator 
supplying  alternating  current.  Two  standard  frequencies  are  usually  resorted  to, 
either  60  or  120  cycles.  By  means  of  rheostats  in  the  field  of  the  motor,  the  speed 
may  be  varied  and  accordingly  the  frequency  also,  thus  allowing  a  little  diversion 
from  the  rated  frequency  of  the  generator.  The  voltage  may  also  be  raised  or 
lowered  by  the  adjusting  of  a  rheostat  in  the  field  winding  of  the  alternator.  Adjust- 
able choke  coils  (inductance  coils)  made  of  heavy  laminated  iron  cores  wound  with 
windings  of  insulated  wire  in  series  with  the  transformer,  are  sometimes  used  in  order 
That  the  transformer  works  to  the  best  advantage  with  the  generator,  or  as  it  is  called, 
"placed  in  resonance  with  each  other." 


Fig.  6. 


Fig.  6  illustrates  a  motor-generator  set  of  the  standard  type.  In  some  instances 
this  set  is  mounted  under  the  operating  table,  while  in  other  installations,  the 
motor-generator  set  is  placed  in  another  room  of  the  wireless  station  so  that  noise 
will  be  far  removed  from  the  operator.  In  land  stations  where  electric  current 
is  not  available  from  power  houses,  a  dynamo,  driven  by  a  gasoline  or  steam  engine 
is  placed  in  a  separate  building.  The  most  practical  method  in  such  stations,  is  to 
have  the  dynamo  furnishing  direct  current  to  storage  batteries,  which  in  turn  supply 
current  to  a  motor-generator  set.  In  this  manner,  the  engine  is  only  operated  a 
few  hours  a  day  in  order  to  charge  the  batteries,  and  the  motor-generator  set  may 
be  started  only  when  a  rnessage  is  to  be  sent. 

The  student  will  remember  that  in  a  previous  lesson  it  was  demonstrated  how 
motors  are  started  by  means  of  a  variable  resistance,  known  as  a  starting  box.  In 
some  instances  a  regular  hand  starting  box  is  employed,  and  is  placed  near  tc  the 
operator  so  that  he  may  operate  it  without  leaving  his  seat.  In  other  instances,  the 
motor  is  started  by  means  of  an  automatic  starter.  The  automatic  starter  consists 
of  a  modified  hand  starter,  but  instead  of  the  lever  being  operated  by  hand,  it  is 
moved  by  a  powerful  electro-magnet.  A  dash  pot  consisting  of  a  metal  cylinder 
fitting  within  another  metal  cylinder  with  oil  between  both,  is  attached  to  the  lever 
so  that  the  electro-magnet  .will  not  be  able  to  pull  the  lever  up  with  a  jerk,  but 
allows  the  lever  to  move  slowly  over  the  contacts.  The  automatic  starter  is  operated 
by  the  closing  of  a  circuit,  which  is  usually  accomplished  by  means  of  a  push  button 
switch,  conveniently  located  near  the  operator  or  on  a  switchboard. 


44 


WIRELESS  COURSE— LESSON  NO.  6 


The  motor-generator  set  is  never  operated  except  when  a  message  is  actually 
being  sent.  If  the  operator  -is  going  to  send  at  successive  intervals  and  only  desires 
to  receive  an  O.  K.  or  other  short  message  in  between,  the  motor-generator  is 
allowed  to  run  continuously,  even  when  the  operator  is  receiving.  The  motor- 
generator  may  be  started  in  a  fraction  of  a  minute,  and  for  this  reason,  it  is  advis- 
able to  keep  it  idle  in  most  cases,  except  when  it  is  to  be  used  as  above  mentioned. 


R      ' 


Fig.  7 


CMOKE  COIL 


Rheostats  are  used  in  the  motor  and  generator  circui-ts  to  give  flexibility  to  the 
set.  In  the  motor  field  circuit,  a  rheostat  is  inserted  so  as  to  enable  the  operator 
to  vary  the  speed  and  consequently  the  frequency  of  the  alternating  current.  In  the 
generator  field  circuit,  which  is  excited  from  the  direct  current  source  which  operates 
the  motor,  another  rheostat  is  inserted  so  as  to  raise  the  voltage  of  the  alternating 
current.  Such  adjustments  are  found  necessary  under  the  varying  conditions  of 
commercial  service.  Fig.  7  gives  a  complete  wiring  diagram  of  a  standard  wireless 
station. 

The  main  difference  between  a  commercial  wireless  station  and  that  of  the 
average  amateur  station  lies  in  the  small  details  which  are  highly  perfected  in  the 
commercial  station.  It  stands  to  reason  that  the  apparatus  in  the  commercial  station 
must  represent  the  highest  development,  and  it  is  constructed  with  a  view  of  obtain- 
ing the  best  results  with  cost  as  a  secondary  consideration.  Commercial  apparatus 
is  accordingly  better  constructed  with  better  attention  paid  to  the  merest  details.  In 
order  to  handle  the  heavy  currents  employed,  the  'apparatus  must  be  of  heavier 
construction  than  that  used  in  amateur  stations.  We  will  therefore  discuss  the 
different  instruments  which  go  to  make  a  commercial  station  transmitter,  from  a 
general  standpoint;  since  each  system  has  slight  variations  in  designs  of  the  various 
instruments. 

The  first  marked  difference  in  construction  between  the  commercial  station  and 
that  of  the  amateur,  is.  the  primary  key.  For  the  modest  purposes  of  most  amateurs 
employing  but  a  small  spark  coil,  the  average  telegraph  key  is  found  excellent. 
However,  in  commercial  practice,  the  heat  of  the  current  passing  between  the  contacts 
would  instantly  fuse  .the  platinum  contact  points  together.  Then  again,  the  rubber 
in  which  these  platinum  contact  points  are  embedded,  would  melt  or  burn. 


Fig.  8 


Fig.  9 


Fig.  8  illustrates  a  standard  type  of  key,  which  can  readily  handle  current  up 
to  3  K.  W.  The  heavy  platinum  contacts  are  of  a  suitable  diameter  to  withstand 
the  heat.  The  lower  one  of  these  is  imbedded  in  mica,  which  withstands  the  heat 
without  damage.  If  heavier  currents  are  to  be  handled,  a  paper  condenser  con- 
taining many  sheets  of  tin  foil  may  be  shunted  across  the  key  contacts,  and  it 
will  then  be  possible  to  operate  this  key  on  currents  of  even  greater  power.  A 
bank  of  lamps  may  also  be  employed  across  the  key  contacts  to  lessen  the  sparking. 

In  some  wireless  stations  a  long  arm  is  attached  on  the  key  lever,  and  passes 
through  a  slot  which  is  cut  in  the  table.-  The  bottom. of  this  lever  has  a  contact 
of  large  diameter  which  touches  another  contact,  both  of  these  being  placed  in  a  tank 
of  oil,  so  that  the  sparking  is  reduced  to  a  minimum.  Other  systems  employ  a 
relay  which  has  very  heavy  contacts,  the  relay  being  operated  by  an  ordinary 


WIRELESS  COURSE— LESSON  NO.  6  45 

telegraph  key.  Such  relays  are  sluggish  in  operation,  and  the  signals  are  not  as 
sharp  as  those  which  may  be  .had  from  directly  operated  key  contacts. 

The  transformer  presents  another  item  which,  though  the  same  in  operation 
as  the  amateur's  transformer,  is  developed  to  a  finer  point.  Most  stations  employ 
a  suitable  type  of  open  core  transformer,  though  the  student  will  remember  that 
the  closed  core  is  far  more  efficient.  In  most  instances  these  transformers  are 
insulated  with  paraffine,  though  in  certain  land  stations  the  transformers  are  placed 
in  oil.  In  the  open  core  transformers,  the  primary  winding  is  arranged  so  that  it 
may  be  taken  out  of  the  coil  with  the  iron  core,  and  rewound  with  mure  turns  if 
desired.  By  winding  more  or  less  turns  on  the  core,  a  condition  is  arrived  at 
where  the  inductance  of  the  generator  armature  and  that  of  the  transformer's  primary 
winding  are  balanced,  so  that  a  very  slight  spark  occurs  at  the  key  contacts.  This 
is  known  as  perfect  resonance.  Closed  core  transformers  are  arranged  quite  often 
with  adjustable  core  parts,  so  that  the  magnetic  field  may  be  varied.  A  switch  with 
a  number  o'f  contacts  also  enables  the  winding  of  the  primary  to  be  varied. 

The  spark  gap,  as  .  in  the  key,  contains  numerous  points  of  superior  design 
and  construction  over  that  used  in  amateur  stations.  Fig.  9  illustrates  the  "electro" 
spark  gap  which  is  capable  of  withstanding  discharges  up  to  3  K.  W.  The  large  rubber 
handle  enables  the  operator  to  adjust  the  gap  while  the  spark  is  passing  between  the 
large  zinc  surfaces.  In  most  gaps  the  zinc  rods  are  equipped  with  radiating  flanges,  so 
that  more  cooling  surface  is  added.  In  commercial  stations  of  large  size,  the  gap 
is  placed  in  a  box  so  that  it  is  muffled.  Compressed  air  is  often  furnished  through  the  .zinc 
rods  so  as  to  cool  the  gap. 

There  is  a  marked  tendency  which  has  been  gaining  favor  since  the  last  few 
years,  to  use  a  gap  which  contains  many  zinc  points  rapidly  revolving  so  as  to 
break  the  discharges  into  a  number  of  smaller  ones.  Fig.  10  illustrates  a  popular 
type.  In  this  gap  a  rotary  disc  of  fibre  is  mounted  on  the  shaft  of  a  small  motor, 
which  may  be  either  run  on  110  volts  or  batteries  as  desired.  A  number  of  zinc 
rods  are  mounted  on  this  fibre  disc,  which  revolves  past  two  stationary  rods  mounted 
on  the  marble  base.  The  advantages  which  are  obtained  with  a  rotary  gap  are 
numerous,  but  the  most  important  one  is;  that  the  emitted  signals  have  a  high  and 
clear  pitch  which  may  be  distinguished  above  the  ordinary  signals,  and  above  the 
rumbling  sound  caused  by  atmospheric  disturbances,  or  commonly  known  as  "static." 
Various  types  of  rotary  gaps  have  been  designed,  but  the  main  feature  common  to 
all  is  the  rotating  member  carrying  the  zinc  rods. 


Fig.  10 

The  condenser  is  one  of  the  most  important  items  and  upon  which  the  success 
of  the  station  depends  to  a  great  extent.  As  in  the  other  details,  the  many  systems 
have  varying  designs  for  the  condenser.  Some  use  plates,  while  others  favor  the 
leyden  jar  type. 

The  plate  condenser  is  one  of  the  most  efficient,  types,  for  it  is  compact  and 
gives  satisfactory  results,  especially  if  the  plates  are  imbedded  in  paraffine.  It  is 
compact,  and  with  intelligent  use  will  not  break  down  under  heavy  currents.  One  of 
the  most  successful  systems  has  the  condensers  made  of  suitable  units  imbedded 
in  insulating  material  and  furnished  with  terminals,  so  that  any  number  of  separate 
units  may  be  used  as  found  necessary  for  the  power  employed.  Plate  condensers 
are  often  arranged  with  the  plates  held  in  a  wooden  rack,  so  that  if  one  should 
accidentally  break  down  under  excessive  current,  it  might  be  removed  without  much 
trouble  and  a  new  plate  substituted. 

The  leyden  jar  type  of  condenser,  as  shown  in  fig.  11,  has  found  more  adherents 
than  the  plate  glass  type,  and  is  used  in  all  of  the  larger  commercial  stations. 
Leyden  jars  of  a  suitable  size  are  used,  which  are  coated  on  both  the  inside  and  out- 
side with  tin  foil.  By  a  novel  process  of  having  silver  melted  into  the  glass,  it  is 
possible  to  have  copper  plating  placed  on  glass,  and  which  will  firmly  hold.  In 
fact,  copper  plated  jars,  such  as  are  used  to-day,  will  withstand  the  scraping  of  a 
knife  on  the  copper  surface  without  more  damage  than  a  slight  scratch.  Copper 


46 


WIRELESS  COURSE— LESSON  NO.  6 


plated  jars  are  somewhat  expensive,  but  as  the  student  has  been  informed,  expense 
is  not  an  item  in  commercial  stations.  .These  copper  plated  jars  have  great  advan- 
tages over  tin  foil  jars,  the  latter  being  subjected  to  many  evils  while  in  actual 
use.  For  instance,  if  a  large  current  is  applied  to  a  tin  foil  coated  jar,  the  tin  foil 
will  blister,  and  as  soon  as  the  coating  separates  itself  from  the  jar,  it  causes  a 


(Courtesy  "Modern  Electrics.") 


Fig.  11 


(Courtesy  "Modern  Electrics.") 


small  spark  to  jump  to  the  glass.  As  this  spark  continues,  the  glass  becomes  weaker 
until  it  is  finally  pierced  and  the  leyclen  jar  rendered  useless.  Copper  plated  jars  can- 
not blister,  and  provided  the  glass  is  of  the  best  grade  for  this  purpose,  the  jars  may 
be  used  for  an  endless  period. 

In  the  earlier  types  of  leyden  jars,  such  as  were  used  for  demonstrating  elec- 
trical principles  in  schools,  a  simple  chain  was  placed  on  the  rod  containing  the 
brass  ball,  to  make  the  inner  connection  to  the  foil.  This  crude  method  could  not 
be  used  in  commercial  practice,  so  that  better  ineans  of  making  connections  have 
been  adopted.  The  inner  connection  usually  consists  of  spring  bands  which  are 
forced  together  while  being  placed  into  the  jar,  ibut  expand  again  making  connec- 
tions with  the  foil  when  released.  The  outer  connections  consist  of  brass  bands 
which  wrap  around  the  foil  making  a  positive  contact.  A  battery  of  leyden  jars  are 
placed  in  a  metal  or  wooden  rack  of  suitable  design,  and  in  some  systems  may  be 
contained  in  a  glass  cabinet. 

The  helix  in  the  commercial  station  varies  but  little  from  that  employed  in 
the  amateur  station.  Often  these  commercial  helices'  will  be  found  to  have  a  hard 
rubber  framework,  which  is  a  great  expense.  Notches  are  cut  into  the  hard  rubber 
parts  so  that  the  heavy  copper  wire  can  fit  into  them.  At  both  ends  of  the  wire 
coil,  small  metal  blocks  are  screwed  on,  which  in  turn  are  screwed  on  to  the  frame- 
work. The  wire  for  the  average  2  K.  W.  station  is  usually  about  number  0  or  00  of  the 
B.  &  S.^auge.  Fibre  frames  are -best. 

In  other  types  of  helices,  hollow  tubing  is  employed  in  place  of  solid  wire, 
since  the  fact  is  well  known  that  the  high  frequency  currents  travel  on  the  surface 
of  wires,  and  not  through  the  center  portion.  Accordingly,  a  copper  or  brass  tube  is 
far  more  desirable.  Instead  of  wooden  or  hard  rubber  frames,  a  type  sometimes 
seen  employs  porcelain  insulators  mounted  on  rods  so  that  the  turns  may  be  wound 
around  this  framework.  Small  metal  clamps  hold  the  turns  in  place,  and  are  them- 
selves held  on  to  the  insulators. 

The  clips  for  the  helix  are  of  many  designs,  but  the  most  serviceable  types  are 
those  in  which  a  jaw  may  be  opened  and  closed  with  either  a  pressure  of  the  hand, 
or  by  unscrewing  a  handle.  The  requirements  for  a  satisfactory  helix  clip  are: 
that  it  should  make  a  good  contact,  and  that  it  should  be  rapidly  adjusted.  Usually 
the  helix  clips  are  supplied  with  insulating  handles,  though  these  are  not  necessary, 
since  the  helix  need  not  be  regulated  while  the  current  is  passing  through  it.  Flexible 
conducting  cord  is  attached  to  the  helix  clips  so  tha,t  the  necessary  connections 
may  be  made.  Tn  other  systems,  the  helix  clips  will  be  found  attached  to  copper 
strips,  which  can  be  placed  at  any  point  of  a  turn  on  the  helix.  Other  helices  are  made 
in  a  different  fashion,  and  the  turns  are  flat,  or  "pan-cake."  The  connection  is  then 
made  by  an  arm  carrying  a  movable  contact,  so  that  by  moving  the  arm  the  contact 
.  will  slide  to  any  point  on  the  wire  which  is  desired. 


WIRELESS  COURSE— LESSON  NO.  6 


47 


Loose-coupled  helices  are  little  used,  though  they  may  be  seen  at  times.  These 
consist  of  two  individual  helices,  each  having  individual  clips  and  conducting  cords. 
One  of  these  helices  is  stationary,  while  the  other  is  mounted  on  rods  so  that  it  may 
slide  further  away  or  nearer  to  the  fixed  helix. 

After  having  described  the  differences  between  commercial  instruments  and  ama- 
.teur  instruments  in  as  brief  a  manner  as  is  permissible  in  the  limited  space,  the 
complete  description  of  a  commercial  station  is  interesting. 

All  the  connections  in  the  secondary  circuit  are  made  with  heavy  stranded  wire  or 
copper  bar.  The  best  installations  are  completely  wired  with  heavy  copper  bar,  so  that 
the  high  frequency  currents  will  have  plenty  of  surface.  Special  precautions  are  taken 
to  have  all  the  connections  thoroughly  insulated  with  porcelain  or  "Electrose"  in- 
sulators, for  the  high  tension  currents  are  apt  to  spark  great  distances. 

Fig.  12  gives  the  complete  wiring  for  a  commercial  station,  and  the  connections 
for  the  primary  circuits  are  already  shown  in  fig.  7.  Four  clips  are  used  on  the 
helix  so  that  the  greatest  variation  possible  is  obtainable  in  the  tuning  of  the  aerial 
and  closed  oscillation  circuits.  A  hot  wire  ammeter  is  placed  in  the  aerial  circuit 
to  denote  when  the  greatest  amount  of  current  is  radiated  into  the  aerial.  In  some 
instances  the  hot  wire  ammeter  is  placed  in  the  ground  instead  of  the  aerial  lead, 
but  the  results  are  equal  and  it  is  a  matter  of  choice.  The  clips  are  moved  on  the 
helix  until  the  hot  wire  ammeter  indicates  the  greatest  amount  of  current,  which 
usually  proves  that  both  circuits  are  in  perfect  resonance.  Hot  wire  ammeters  such 
as  are  extensively  used  in  wireless  work  to  ascertain  the  strength  of  the  radiated  aerial 
current,  have  a  short  section  of  platinum  or  other  wire  arranged  to  react 
on  an  indicating  needle  so  that  whenever  a  certain  current  strength  passes  through 
it,  it  will  be  more  or  less  heated  and  consequently  elongated  causing  the  needle  to 
deflect  over  the  graduated  scale'. 

The  lead  to  the  aerial  from  the  aerial  switch  is  passed  through  a  heavy  porcelain 
tube  or  electrose  insulator,  known  as  the  "lead-in."  The  lead  should  be  of  heavy 
copper  stranded  cable,  and  insulated  with  a  heavy  coating  of  rubber.  On  the  outside 
of  the  lead-in,  the  leads  to  the  aerial  are  connected.  Thus  the  set  is  completed. 


Fig.  12 


During  thunder  storms,  it  is  advisable  to  ground  the  aerial,  so  that  no  damage 
will  be  caused  by  the  heavy  lightning.  This  is  accomplished  by  the  use  of  a  single 
pole,  double  throw  switch  as  illustrated  in  fig.  13.  It  will  be  noted  that  the  center 
hinge  post  of  the  switch  is  connected  to  the  aerial  lead,  while  the  top  post  is  con- 
nected to  the  transmitting  set,  and  the  other  post  to'  the  ground.  By  throwing  .the 
switch  lever  to  the  ground,  the  station  is  safe  from  lightning  damages.  Commercial 
stations  often  have  this  switch  placed  on  the  outside  of  the  building,  near  the 
lead-in,  which  is  the  most  logical  place  to  have  it,  since  the  lightning  discharge  would 
not  pass  around  the  curves  of  the  wire,  and  instead  would  leak  off  the  wires  and 
cause  great  damage. 


48 


WIRELESS  COURSE— LESSON  NO.  6 


Fig.   14  illustrates  a  typical  wireless  station.     The   student  will  note  the  location 
and  arrangement  of  the  various  instruments  which  have  been  described. 

Within  the  last  four  years,  new  wireless  systems  operating  upon  new  principles 


w 


TO 
INSTRUMENTS 


SWITCH 
OUTSIDE 
OF  B'LD'S. 


Fig. 


have  become  common,  and  in  fact  are  threatening  the  continued  use  of  the  regular 
spark  systems.  These  new  systems  possess  many  distinct  advantages  which  could 
not  be  had  with  the  older  systems.  In  the  following  lesson,  the  student  will  be 


'Fig.  14  (Courtesy  "Modern  Electrics.") 

given  a  brief  description  of  the  Telefunken,  Von  Lepel,  and  the  Poulsen  systems, 
which  represent  a  novel  departure  from  the  standard  Marconi  spark  system,  so  well 
known  to  all. 


WIRELESS  COURSE— LESSON  NO.  7  49 


NEW  TRANSMITTING  SYSTEMS. 

•  ITHIN  the  last  few  years  new  systems  have  been  introduced  for  producing  elec- 
trical oscillations  for  wireless  transmission.  These  systems  have  proven 
superior  to  the  older  spark  system  which  is  universally  employed  to-day,  and 
in  fact,  it  is  probably  a  matter  of  a  short  time  when  all  the  stations  will  be  employing 
the  more  efficient  newer  systems. 

Aside  from  the  regular  Marconi  spark  system,  there  are  two  other  methods  of 
producing  oscillations  for  wireless  purposes  used  at  present  in  commercial  work: 
The  Quenched  spark  system,  and  the  Arc  system.  Under  the  former  heading,  the 
Telefunken  and  Yon  Lepel  systems  operate;  while  under  the  latter  system  we  find 
the  famous  Poulsen  system,  which  is  also  used  for  wireless  telephony. 

The  Telefunken  system,  which  has  been  introduced  by  the  Telefunken  Company 
in  Germany,  has  been  the  beginning  of  a  new  era  in  wireless  telegraphy,  and  has 
awakened  the  public  to  the  greater  possibilities  which  may  be  expected  of  wireless 
transmission  in  the  future.  With  this  quenched  spark  system  it  is  possible  to  send 
wireless  messages  at  three  times  the  range  procurable  with  an  equal  amount  of  power 
using  the  older  systems.  The  spark  produced  is  of  a  perfect  musical  pitch,  and  can 
be  distinguished  .above  the  rumbling  of  static  electricity  in  the  air.  and  above  the 
interference  of  other  stations.  In  fact,  it  _is  the  only  system  aside  from  the  Poulseii, 
Fessenden,  and  the  Von  Lepel  systems  in  which  tuning  can  be  accomplished  to  a 
degree  of  satisfaction  under  the  trying  conditions  of  commercial  service. 

The  novel  feature  in  the  Telefunken  quenched  spark  system  is  in  the  spark  gap, 
which  is  entirely  original  in  design.  This  gap  causes  the  oscillating  circuit  and  the 
aerial  circuit  to  react  upon  each  other  in  such  a  manner  as  to  produce  the  greatest 
effect,  the  action  being"  explained  in  the  following  extract  taken  from  "Modern 
Electrics,"  page  775,  of  Volume  No.  4: 


J, 

/^^^ 


Fig.  1  Fig.  2 

(Courtesy  "Modern   Klectrics.") 

"Most  operators  have,  no  doubt,  noticed  that  stations  using  the  ordinary  spark- 
gap  can  be  heard  in  .two  places  on  their  tuners,  in  other  words,  these  stations  each 
seem  to  have  two  different  wave  lengths  at  the  same  time.  In  reality  there  are  two 
wave  lengths  present,  even  when  the  aerial  and  condenser  circuits  are  tuned  to  the 
s'Miie  wave  length,  and  neither  wave  is  that  to  which  the  two  circuits  are  tuned.  This 
double  Wave  results  from  an  interchange  of  energy  between  the  condenser  and 
aerial  circuits.  Following  the  initial  discharge  of  the  condenser,  the  primary  (con- 
denser) circuit  starts  oscillating,  the  oscillations  increasing  to  a  maximum  value 
at  which  point  the  secondary  (aerial)  circuit  begins  to  oscillate  .and  gradually 
increases  to  a  maximum.  Meanwhile  the  primary  oscillations  are  decreasing  in  value 
and  become  zero  at  the  time  the  secondary  oscillations  reach  their  maximum.  The 
primary  then  begins  oscillating  again,  as  before,  but  the  energy  necessary  is  not 
supplied  by  the  power  transformer  but  is  taken  from  the  aerial  circuit,  which  causes 
the  secondary  oscillations  to  die  down,  to  zero  at  the  time  the  primary  oscillations 
reach  their  second  maximum,  which,  however,  is  lower  than  the  first.  This  is  illus- 
trated in  fig.  1. 

"This  interchange  of  energy  continues  until  the  oscillations  of  both  circuits 
decrease  to  a  point  where  the  current  in  the  primary  circuit  is  no  longer  able  to 
jump  the  spark  gap.  Then  the  oscillations  in  the  secondary  circuit  slowly  die  out 
but  are  too  feeble  to  radiate  much  energy  from  tin-  aerial.  The  result  of  this  is  that 
the  aerial  circuit,  instead  of  radiating  a  strong  train  of  waves  for  each  discharge 
of  the  condenser,  radiates  a  number  of  short  wave  trains  whose  aggregate  value  is 
much  below  that  of  a  single  peaked  long,  .slightly  damped  wave  train  that  would  result 
if  the  oscillations  in  the -primary  circuit  be  stopped  just  as  soon  as  the  secondary 
oscillations  reach  their  maximum  value,  .as  shown  in  fig.  2. 

"In  order  to  radiate  the  most  energy  from  the  aerial,,  it  is  essential  that  the 
primary  remain  active  long  enough  to  build  up  the  secondary  oscillations  to  a  maxi- 
•num.  If,  at  this  point,  the  spark  gap  can  be  made  to  lose  its  conductivity,  the 


op\  i-i-lit    T.H2  ]>v   K.   I.  Co. 


50 


WIRELESS  COURSE— LESSON  NO.  7 


energy  in  the  secondary  will  not  be  lost  in  setting  the  primary  circuit  oscillating  again, 
but  will  be  radiated  from  the  aerial. 

"There  are  several  forms  of  spark  gap  which  possess  this  desirable  property 
of  promptly  damping  out  the  primary  oscillations.  The  most  widely  known  is  prob- 
ably the  rotary  gap  (which  has  been  explained  in  the  previous  lesson),  and  which 
was  introduced  originally  by  Marconi,  and  then  there  are  the  quenched  gaps  of  Von 
Lepel,  Peukert,  the  Telefunken  Company,  and  others,  which  operate  on  the  principles 
first  made  known  by  Professor  Max  Wein  in  1906,  and  the  Mercury  Vapor  discharger 
of  Cooper-Hewitt." 

The  student  will  be  given  a  thorough  explanation  of  the  quenched  spark  system 
used  at  present  by  the  Telefunken  Company  in  such  manner  as  the  limited  space 
allows. 

The  Telefunken  quenched  spark  gap  consists  of  a  series  of  copper  plates  which 
are  so  arranged  that  their  center  faces  are  raised,  as  shown  in  fig.  3.  This  is  accom- 
plished by  having  the  'ridges  turned  out  near  the  edges  of  the  plates,  and  by  placing 
mica  rings  of  slight  thickness  between  the  two  ridges  of  adjacent  plates,  a  very  small 
gap,  (0.01  inch),  is  introduced.  In  fig.  3  the  student  will  note  the  mica  rings  and 
the  very  slight  gap  which  is  formed  between  the  plates.  Usually  1.200  volts  are 
allowed  to  each  gap,  and  as  many  are  placed  in  series  as  necessary.  In  the  standard 
Telefunken  sets,  the  gap  is  composed  of  a  number  of  copper  discs  clamped  together 
in  a  special  framework,  and  each  gap  is  provided  with  a  metal  spring  piece  which 
is  inserted  between  the  gaps  which  are  to  be  short-circuited.  If  a  nearby  station 
is  to  be  called,  the  operator  lowers  the  voltage  of  his  generator,  and  short-circuits 
a  few  gaps,  leaving  only  one  or  two.  In  this  manner  the  signals  are  reduced  to 
such  a  point  as  to  reach  the  neighboring  station  without  disturbing  the  other  stations 
within  the  usual  range.  The  center  raised  portion  of  the  Telefunken  copper  discs 
is  made  of  silver  which  has  been  welded  on  the  copper. 

In  all  of  the  larger  sets,  the  copper  plates  are  single  faced,  the  raised  portion 
being  on  only  one  side,  while  the  other  side  of  the  plate  is  perfectly  flat.  The  plate 
is  then  placed  into  the  countersunk  portion  of  a  large  bronze  plate  which  serves 
the  purpose  of  adding  more  cooling  surface  to  the  plate.  These  extra  cooling  plates 
are  necessary,  since  the  sparks  can  be  quenched  with  better  efficiency  while  the 
gap  remains  reasonably  cool.  The  gap  is  shown  in  fig.  4. 


Fii 


Fig.  4 


(Courtesy  "Modern  Electrics.") 


While  the  gap  is  in  operation  the  sound  of  the  sparks  does  not  resemble  the 
loud  crashing  sound  of  the  regular  spark  sets,  but  instead  a  faint  sound  like  escaping 
steam  may  be  barely  heard  at  a  distance  of  less  than  10  feet  from  the  gap.  On  ship- 
hoard  this  system  is  particularly  desirable,  since  the  signals  cannot  be  read  from 
sound  by  an  unauthorized  person  located  near  the  wireless  room. 

After  describing  the  gap  which  forms  the  vital  feature  of  the  Telefunken  system, 
a  description  of  the  other  parts  of  this  system  is  naturally  of  interest.  The  power 
is  supplied  to  the  gap  at  a  voltage  of  about  6,000  volts,  and  is  furnished  by  a  closed 
core  transformer  of  very  small  dimensions.  The  efficiency  of  this  transformer  is 
extremely  high,  and  but  a  very  slight  percentage  of  power  is  lost  in  the  transforma- 
tion of  the  voltage.  A  500  cycle  generator  supplies  current  at  110  or  220  volts 
to  this  transformer  through  a  simple  telegraph  key.  This  generator  is  another  feature 
of  the  set  which  is  extremely  novel,  for  the  obtaining  of  such  high  frequency  current 
from  a  small  size  generator  is  a  problem  requiring  much  experimenting  and  design- 
ing. This  generator  has  the  two  windings,  both  field  and  armature,  mounted  on  pole 
pieces  which  are  attached  to  the  iron  frame.  Between  the  poles  on  which  these 
windings  are  placed,  a  mass  of  laminated  iron  with  many  teeth,  revolves,  driven 
by  either  a  directly  coupled  electric  motor  or  an  engine.  In  instances  where  a  motor 
is  used,  the  motor  is  supplied  with  a  field  rheostat  of  a  soecial  type  so  that  the  speed 
of  the  motor  may  be  carefullv  varied.  This  rheostat  is  similar  to  a  tuning  coil,  being 
wound  on  a  cylinder  about  10  inches  long,  and  fitted  with  a  sliding  contact  mounted 
on  a  rod.  By  moving  the  slider  a  slight  distance,  one  turn  or  more  can  be  inter- 
posed into  the  field  circuit,  with  the  resulting  slight  difference  in  speed  of  the  motor. 
Ry  moving  this  rheostat  handle,  the  pitch  of  the  spark  is  changed,  and  likewise 
the  emitted  signal.  This  is  a  very  valuable  characteristic,  especially  so  in  war 


WIRELESS  COURSE— LESSON  NO.  7 


51 


operations,  inasmuch  as  a  station  can  change  its  spark  and  disguise  its  identity.  A 
coil  of  wire  mounted  on  a  handle  and  connected  across  a  pair  of  telephone  receivers 
and  detector  is  used  by  the  operator  for  determining  the  pitch  of  the  signals  being 
transmitted  by  the  station. 

The  condenser  used  in  connection  with  the  transformer  and  spark  gap  is  also 
a  novelty,  since  it  uses  heavy  paraffined  paper  for  the  dielectric,  in  place  of  the  glass 
plates  usually  employed.  The  voltage  being  only  6,000  volts  as  against  the  25,000 
volts  used  in  the  regular  spark  systems,  enables  heavy  paraffined  paper  to  be  suffi- 
ciently strong  electrically,  to  withstand  the  voltage.  The  condenser  made  of  these 
paraffined  paper  sheets  is  mounted  in  a  neat  wooden  case  and  placed  in  the  framework 
holding  the  spark  gap  and  tuning  instruments.  In  larger  sets  the  leyden  jars  are  used 
but  for  sets  of  2  K.  W.  or  smaller  the  paper  condensers  are  satisfactory. 

In  tig.  5  will  be  seen  a  wiring  diagram  of  the  Telefunken  system,  and  it  will  be 
immediately  noticed  that  no  helix  arrangement  is  used  for  the  connecting  of  the 
oscillation  and  aerial  circuits.  Instead,  the  aerial  and  oscillation  circuits  are  separately 
tuned  by  independent  inductance  producers  known  as  "Variometers."  These  vario- 
meters operate  on  the  well  known  and  previously  described  principle  of  self  induc- 
tion. The  student  has  learned  that  a  wire  produces  in  itself  a  certain  amount  of 
self  induction  and  that  this  induction  may  be  increased  by  forming  the  wire  around 


6  "=• 


Fig.  5 


into  a  coil.  See  cut  of  variometer,  fig.  6.  The  variometer,  which  is  used  mostly  in 
receiving  instruments,  consists  of  generally  two  coils  connected  in  series,  and  so 
arranged  that  the  inductance  between  the  coils  may  be  increased  or  decreased  by 
having  the  coils  opposing  each  other  or  arranged  so  as  to  aid  each  other,  and  thus 
increase  the  self  inductance.  In  the  Telefunken  variometers  as  used  for  transmitting, 
four  coils  are  arranged,  two  in  an  upper  frame,  and  two  in  a  lower  frame.  These 
frames  are  round  in  shape,  and  mounted  so  that  the  upper  one  rotates  on  its  axis, 
while  the  lower  one  is  stationary.  The  edge  of  the  rotating  upper  disc  is  marked 
in  degrees  of  a  circle,  so  that  by  turning  in  one  direction,  the  inductance  will  be 
at  the  maximum  when  the  pointer  indicates  1-80  degrees.  However,  by  revolving  the 
disc  in  the  opposite  direction,  the  inductance  is  decreased,  and  consequently  the 
wave-length.  By  a  special  switch,  a  certain  combination  of  the  windings  can  be 
obtained  so  as  to  secure  different  inductance  effects.  Two  of  these  variometers 
are  fitted  to  the  apparatus,  one  in  the  oscillating  circuit,  and  the  other  in  the  aerial 
circuit.  Besides  the  inductance  furnished  in  the  aerial  circuit  by  the  one  variometer, 
a  series  of  coils  are  mounted  on  a  framework  and  arranged  with  a  flexible  cord 
and  plug  contact,  so  that  these  coils  may  be  added  in  the  aerial  circuit  to  increase 


52  WIRELESS  COURSE— LESSON  NO.  7 

the  wave-length  up  to  2,000  meters  if  desired.  In  the  ground  connection,'  a  hot 
wire  ammeter  is  mounted,  so  that  the  two  variometers  may  be  turned  until  the 
hot  wire  ammeter  indicates  the  greatest  deflection.  In  a  2  K.  W.  set  this  deflec- 
tion will  be  about  18  amperes. 

The  transmitter  may  be  tuned  with  a  wave-metei",  by  moving  the  variometer 
in  the  oscillation  circuit  until  the  circuit  is  tuned  to  a  desired  wave-length.  The 
variometer  in  the  aerial  circuit  is  then  turned  until  the  hot-wire  ammeter  indicates 
the  greatest  deflection,  the  set'then  emitting  the  wave-length  desired.  The  flexibility 
of  the  set  is  without  equal,  for  any  wave-length  may  be  obtained  in  an  instant  with 
the  adjusting  of  the  variometers. 

Approximately  three  times  the  range  may  be  obtained  with  the  Telefunken 
quenched  spark  system  over  that  obtained  with  the  regular  spark  system.  The  receiv- 
ing instruments  are  likewise  vastly  superior  to  those  employed  with  ordinary  spark 
systems. 

By  means  of  the  mono-tone  telephone  receiver,  signals  may  be  received  that 
are  absolutely  non-interferable,  even  if  a  spark  station  be  located  in  the  immediate 
neighborhood  of  the  receiving  station.  The  mono-tone  telephone  receiver  consists 
of  a  strip  of  steel  which  is  tuned  to  vibrate  for  a  certain  electrical  frequency.  When 


(Courtesy  "Modern  Electrics.") 
Fig.  6 


a  spark  is  emitted  by  the  transmitter,  if  it  be  of  the  same  frequency  as  the  strip 
in  the  telephone  receiver,  it  will  operate  same.  All  quenched  sparks  having  a  lower 
or  higher  pitch  will  not  effect  the  receiver.  Spark  sets  of  the1  regular  type  will  not 
operate  the  receiver  at  all.  Thus,  absolute  selectivity  may  be  obtained,  except  if 
another  quenched  spark  station  would  seek  to  interfere  intentionally.  An  instru- 
ment known  as  a  resonance  relay  enables  the  operator  to  receive  signals  on  a 
standard  recorder,  so  that  the  signals  will  be  printed  on  a  paper  tape.  A  small 
bell  can  also  be  caused  to  ring  so  that  the  operator  is  informed  that  he  is  being 
called.  These  possibilities  were  not  found  in  the  older  sets,  although  a  bell  ana 
tape  recorder  could  be  used  for  very  slight  distances.  In  the  quenched  spark  system 
these  instruments  may  be  worked  at  ranges  of  several  hundred  miles,  and  in  fact  as 
far  as  the  transmitter  can  operate  the  ordinary  telephone  receivers  usually  employed. 
l!y  means  of  a  specially  arranged  clock-work,  the  bell  will  only  respond  when  a 
predetermined  number  of  dots  or  dashes  are  sent  by  a  quenched  spark  transmitter 
tuned  both  in  pitch  and  in  wave-length  to  the  calling  apparatus  in  the  receiving 


station. 


WIRELESS  COURSE— LESSON  NO.  7 


53 


The  Von  Lepel  system  varies  but  little  from  the  Telefunken  system,  the  prin- 
ciple of  operation  being  the  same,  .though  the  execution  of  the  idea  is  slightly  different. 

In  1907,  the  Von  Lepel  system  of  producing  wireless  waves  was  introduced 
by  Baron  Von  Lepel  of  Germany,  and  during  1908  and  1909,  a  continuous  controversy 
•was  engaged  in  between  the  Von  Lepel  interests  and  the  Telefunken  Company  as 
to  the  originality  of  the  rival  systems.  These  debates  were  printed  in  the  English 
"Electrician"  and  were  followed  by  all  those  interested  in  wireless  telegraphy,  though 
the  final  results  as  to  which  system  had  the  priority  in  the  quenched  spark  appli- 
cation to  wireless  telegraphy  apparatus,  could  not  be '  definitely  decided.  Both  the 
Telefunken  Company  and  the  Von  Lepel  interests  have  many  patents  in  Germany 
on  presumably  similar  inventions. 

The  new  and  important  feature  of  the  Von  Lepel  system  consists  of  its  quenched 
spark  gap.  This  gap  is  made  of  two  copper  discs  which  are  separated  by  a  piece 
of  ordinary  paper,  or  perhaps  two  sheets  may  be  used  if  desired.  A  small  hole  has 
been  made  in  the  center  of  the  paper.  The  copper  discs  are  'then  tightly  clamped 
together  so  that  no  air  can  enter.  An  arc  or  spark  forms  between  the  two  copper 
discs  where  the  paper  is  removed,  and  as  the  arc  continues  to  operate  for  two  or 
three  hours,  the  paper  finally  becomes  entirely  consumed  and  must  be  replaced.  The 
burning  of  the  paper  furnishes  additional  advantages  for  the  arc.  The  space  between 
the  copper  discs  is  said  to  be  .002  inch,  while  the  plates  are  3  inches  in  diameter. 


WA 


In  the  larger  forms  of  the  Von  Lepel  spark  gap,  the  copper  discs  are  water  cooled. 
The  arc  or  spark  gap  may  operate  on  very  low  direct  current  voltages,  since  the  gap 
is  separated  by  such  a  small  distance.  Whether  the  discharge  takes  place  in  the 
form  of  an  arc  or  in  the  form  of  sparks  is  a  question  which  is  still  discussed  with 
uncertainty.  It  is  probably  safe  to  presume  that  the  discharge  is  an  arc,  and  that 
the  burning  paper  furnishes  hydrogen  to  this  arc,  thus  steadying  it  in  constancy  of 
operation.  It  has  been  claimed  that  with  the  Von  Lepel  system  it  is  possible  to 
cover  ranges  of  300  miles  with  less  than  l/2  K.  VV.  of  primary  power.  Should  this 
be  correct,  there  is  but  little  doubt  that  it  is  the  most  efficient  system  in  use  at  the 
present  time,  including  the  Telefunken  quenched  spark  system. 

The  arc  operates  on  currents  as  low  as  300  to  500  volts,  a  transformer  being 
unnecessary  if  a  motor-generator  set  is  employed  to  raise  the  current.  Direct  cur- 
rent is  employed  at  a  consumption  of  1  to  2  amperes.  Owing  to  the  extreme  simpli- 
city of  the  Von  Lepel  instruments,  it  is  admirably  adapted  for  portable  purposes. 
As  in  the  Telefunken  system,  the  condenser  is  made  of  mica  or  paraffined  paper, 
but  is  only  4  cubic  inches  in  dimensions. 


54  WIRELESS  COURSE  —LESSON  NO.  7 

The  wiring  diagram  of  the  Von  Lepel  system  shown  in  fig.  7  illustrates  the 
connections.  It  will  be  noted  that  as  in  the  Telefunken  system,  the  oscillation 
circuit  is  separately  tuned  by  its  own  inductance  while  the  aerial  also  is  separately 
tuned  and  has  an  additional  aerial  inductance  for  long  wave-lengths. 

The  Poulsen  system  introduced  by  Valdemar  Poulsen,  a  Dane,  in  1903.  is  based 
on  the  arc  principle  of  producing  electrical  oscillations,  and  is  used  to-day  with 
much  success.  It  possesses  many  advantages  in  common  with  the  Telefunken  quenched 
spark  system. 

The  Poulsen  system  is  based  on  the  experiments  performed  by  Duddell  in  1900, 
in  which  an  arc  was  made  to  produce  electrical  oscillations  and  give  out  a  musical 
note  when  shunted  with  an  inductance  and  condenser.  It  has  since  been  called  the 
singing  arc.  Fig.  8  illustrates  the  Duddell  singing  arc  hook-up,  in  which  it  will  be 
noted  that  a  choke  coil  is  used  to  prevent  the  oscillations  from  backing  through 
the  generator,  and  instead  are  made  to  charge  the  condenser  and  then  discharge 
through  the  inductance  and  arc.  The  following  explanation  illustrates  the  reason 
why  electrical  oscillations  are  formed  when  an  arc  is  shunted  by  a  capacity  and 
inductance. 

It  is  known  that  with  an  increase  of  current  through  an  arc  tho  voltage  between 
the  arc  terminals  decreases.  For  this  reason,  when  the  arc  is  connected  in  series 
with  a  source  of  voltage  and  the  current  turned  on  into  the  arc,  this  current  tends 
to  increase  to  a  very  large  value,  and  for  this  reason  resistances  are  usually  inter- 
posed in  the  power  leads  of  arc  lamps.  If  the  capacity  and  inductance  are  now 
shunted  around  the  arc.  the  condenser  begins  to  charge.  This  takes  current  from 
the  arc  and  in  consequence  the  voltage  between  the  arc  terminals  increases,  and 
causes  more  current  to  flow  into  the  condenser,  since  it  is  barred  by  the  increasing 
voltage  difference  between  the  terminals  of  the  arc.  Finally  the  condenser  becomes 
charged  to  an  equal  potential  to  that  of  the  arc,  but  owing  to  the  inductance  in  the 
circuit,  the  charging  of  the  conden*""  continues  for  a  time  after  this  period.  The 
result  is  that  the  condenser  has  a  higher  potential  difference  than  the  arc,  which 
causes  the  current  to  cease  flowing  into  the  condenser.  The  condenser  then  begins 
to  discharge  through  the  arc,  causing  a  drop  in  the  arc  voltage,  and  a  further 

CO/JL 


UJ  JO 


vwwwv 


Fig.  8 

discharge  of  the  condenser.  While  the  condenser  is  discharging,  the  inductance  in 
series  with  the  condenser  tends  to  preserve  the  discharging  current,  so  that  the 
condenser  potential  finally  falls  below  that  of  the.  arc.  After  a  minimum  potential 
in  the  condenser  has  been  reached  by  this  discharging,  the  process  is  reversed  and 
the  action  begins  anew.  The  arc  and  the  condenser  circuit  are  thus  in  an  unstable 
condition  and  the  condenser  continues  to  charge  and  discharge,  thus  impoverishing 
and  replenishing  the  arc  as  to  current.  Whatever  energy  is  expended  in  this  oscilla- 
tion circuit  is  drawn  from  the  direct  current  source.  It  is  well  to  mention  here 
that  alternating  current  cannot  be  used  on  the  arc  for  wireless  purposes. 

In  the  Duddell  arc  the  period  of  the  oscillations  was  not  sufficiently  rapid  to 
enable  their  use  in  wireless  telegraphy.  The  improvements  of  Poulsen  made  the 
application  possible,  and  to-day  this  system  ranks  among  the  foremost  for  efficiency 
and  advantages'. 

The  main  difference  between  the  Poulsen  and  the  plain  Duddell  arc,  is  that 
the  former  is  so  arranged  that  the  arc  takes  place  between  a  solid  carbon  electrode, 
and  a  hollow  copper  vessel  in  which  a  continuous  current  of  cold  water  is  caused  to 
flow.  This  keeps  the  arc  cooled,  and  the  arc  is  steadied  by  being  enclosed  in  a 
chamber  to  which  hydrogen  gas  is  supplied.  In  some  types  the  carbon  electrode 
is  slowly  rotated  by  a  motor,  and  two  powerful  electro-magnet  poles  cause  the 
frequency  of  the  oscillations  to  be  greatly  increased.  The  arc  no  longer  emits  a 
musical  note,  since  the  rapidity  of  the  oscillations  has  increased  to  beyond  the  range 
of  the  human  ear,  and  are,  therefore,  inaudible. 


WIRELESS  COURSE— LESSON  NO.  7  55 

Fig.  9  illustrates  the  principle  of  connections  employed  in  the  Poulsen  system. 
The  oscillation  circuit  is  connected  to  the  aerial  circuit  by  a  loose-coupled  trans- 
former. The  condenser  consists  of  a  number  of  brass  plates  mounted  on  a  rotary 
:-lrift  so  that  these  plates  may  be  turned  in  order  to  intersect  other  plates,  the  whole 
being  immersed  in  oil.  The  current  is  furnished  at  low  voltage  (under  110  volts), 
but  i«  some  of  the  Poulsen  arcs  a  voltage  of  550  volts  has  been  employed. 


ig.  9 


The  oscillations  produced  by  the  arc  system  are  exceedingly  sharp  and  require 
accurate  tuning  at  the  receiving  end.  Inasmuch  as  the  signals  produced  are  beyond 
the  range  of  audibility,  some  means  must  be  employed  to  transform  these  received 
oscillations  to  a  lower  period  so  that  they  may  be  heard.  This  is  accomplished  by 
a  clever  arrangement  known  as  the  "ticker.'*  The  ticker  consists  of  a  clever  little 
automatic  switch  device  which  causes  the  current  sent  through  the  detector  to  be 
interrupted  so  that  it  may  charge  a  condenser,  and  this  condenser  in  turn  discharges 
through  the  detector;  and  being  that  the  discharges  are  of  a  much  lower  frequency 
than  the  original  oscillations,  the  signals  can  be  heard  in  the  telephone  receivers 
on  the  operator's  head.  All  other  spark  stations  cannot  be  heard,  even  if  they  are 
located  in  the  immediate  neighborhood. 

By  supplanting  the  key  with  a  telephone  transmitter,  the  set  is  capable  of  being 
used  for  wireless  telephony.  In  the  De  Forest  system,  which  operates  a  wire- 
less telephone  on  the  same  principle,  a  clever  method  is  used  to  break  up 
the  oscillations  so  that  they  may  he  received  by  ordinary  stations.  This  consists 
of  a  buzzer  having  heavy  contacts  mounted  on  the  vibrating  armature.  The  buzzer 
operates  with  a  Few  dry  cells  arid  a  simple  kev.  while  tbe  aerial  is  connected  in  series 
with  the  heavy  contacts.  The  results  are  that  f^e  Oscillations  are  broken  up  so  that 
they  may  be  heard  by  afiv  station  ecwirmed  with  ordinary  receiving  armaratus.  This 
is  known  as  the  "chopper  set."  In  this  manner  the  operator  may  call  up  with  the 
wireless  telephone  or  teles-ranh  using  the  same  set. 

The  Poulsen  system  is  used  largely  in  Europe  and  gives  excellent  results.  How- 
ever, it  is  a  matter  of  doubt  whether  it  can  'compare  to  the  Telefunken  system, 
which  is  more  stable,  smce  it  does  not  recmire  rotarv  parts  in  the  gap,  nor  gases  and 
ndjustments.  The  Poulsen  system  offers  remarkable  tuning  advantages,  which  have 
never  been  duplicated. 


56 


WIRELESS  COURSE— LESSON  NO.  7. 


HWVi 


TELEODAPW 


nct     — Srorre» 


POUL5EIN 


ClBCUlTJi 


(Courtesy  "Modern  Electrics.") 


The  Poulsen  apparatus,  as  used  by  the  Federal  Telegraph  Co.,  works  practically 
as  follows:  The  arc  is  formed  in  an  atmosphere  of  coal  gas  or  other  hydrocarbon 
gas  in  an  air  tight  chamber,  between  the  poles  of  a  strong  electro-magnet.  The  mag- 
net coils  may  also  be  used  as  choke  coils  to  prevent  oscillations  passing  back  into 
the  generator,  or  additional  choke  coils  may  be  inserted.  The  voltage  used  is  about 
500  volts,  D.  C,  the  copper  electrode  and  arc  chamber  being  cooled  by  water 
circulation. 

The  oscillation  circuit  is  formed  by  connecting  one  electrode  direct  to  the  earth 
connection,  and  connecting  the  other  pole  to  the  antenna  through  a  large  inductance. 
The  condenser,  in  this  case,  is  the  capacity  of  the  antenna  and  earth. 

The  Morse  key  is  arranged  to  cut  in  a  few  more  turns  of  inductance  when  de- 
pressed, thus  giving  out  a  longer  wave.  This  accounts  for  the  unreadable  signals 
heard  by  many  amateurs,  who  cannot  tune  to  the  longer,  or  working  wave,  and 
only  hear  the  shorter,  or  compensating  wave,  when  the  key  is  up.  The  working 
wave  is  generally  2,GtX)  to  3,000  meters  long. 

The  receiving  apparatus  differs  from  the  ordinary,  in  that  it  has  no  detector.  As 
the  frequency  used,  is  of  course,  so  high'  as  to  be  practically  inaudible  to  the  ear,  it 
must  be  broken  up  to  be  audible.  This  is  accomplished  by  a  device  called  a  "ticker," 
as  aforementioned,  which  is  merely  an  interrupter  capable  of  special  adjustments, 
placed  in  series  with  a  small  condenser,  around  which  is  shunted  a  pair  of  low  resist- 
ance phones.  Across  the  ticker  and  small  condenser  is  shunted  a  variable  condenser 
The  received  oscillations  charge  the  variable  condenser  when  the  ticker  is  open.  Upon 
its  closing,  the  variable  condenser  discharges  into  the  small  condenser.  When  the. 
ticker  again  opens,  the  small  condenser  discharges  into  the  phones,  causing  the  signals 
to  be  heard.  The  ordinary  low  frequency  spark  cannot,  of  course,  be  heard  on  this 
arrangement,  but  tlie  quenched  spark,  or  so-called  "sparkless"  system  can  he. 

Great  advantages  are  claimed  for  the  Poulsen  system,  such  as  its  noiselessness, 
the  ease  of  handling  high-powered  sets,  the  absence  of  high  voltages,  -etc.  It  is 
claimed,  also,  that  greater  distances  may  be  covered  overland  with  this  system,  and 
the  work  being  done  by  the  Federal  Company  shows  this  to  be  true,  as  they  con- 
stantly work  from  500  to  900  miles  overland  in  daylight.  (See  lesson  18.) 

As  we  stated  at  the  beo-inning  of  this  lesson,  it  is  only-  a  matter  of  time  when 
the  later  systems  described  in  this  lesson  will  supersede  the  ordinary  spark  system. 
These  later  systems  have  only  given  us  an  idea  as  to  what  may  be  expected  in  the 
future,  when  even  electrical  energy  -may  be  transmitted  wirelessly  without  loss  of 
power  to  any  considerable  degree.  To  the  student  and  experimenter,  it  demonstrates 
.  clearly  the  remarkable  field  opened  for  research  in  this  branch  of  science. 


WIRELESS  COURSE— LESSON  NO.  8 


Lesson  Number  Eight 


RECEIVING  APPARATA. 
PART  ONE. 

E    various    instruments    or    apparata    brought    into    play,    in    the    receiving^  of 
\\    wireless  messages,  has  been  much  improved  upon  since  Commendatore  William 
•^   Marconi  sent  his  immortal  three  dots,  representing  the  Morse  code  letter  "S," 
across    the    broad    Atlantic    in    1901.  . 

It  will  probably  be  the  best  plan,  to  first  explain  the  function  and  actions  of  a 
simple  receiving  outfit,  such  as  that  employed  in  the  smallest  amateur  or  experimental 
station.  In  fig^  1,  is  shown  such  a  layout,  including  the  aerial  wire,  a  detector  D, 
telephone  receiver  R,  and  ground  connection  G.  This  forms  the  very  simplest 
receptor  for  wireless  signals  possible. 


Fig.  1. 

The  incoming  oscillations  induced  in  the  aerial  wire,  pass  through  the  detector 
or  cymoscope,  as  Prof.  J.  A.  Fleming  has  termed  them,  and  on  down  to  earth. 
The  detector,  which  in  these  discussions  will  be  considered  one  of  the  modern 
crystal  rectifying  type,  such  as  the  silicon  or  perikon,  tends  to  act  as  an  electrolytic 
valve,  and  permits  the  currents  coming  in  one  direction  to  traverse  it  many  times 
better  than  currents  from  the  opposite  direction,  or  polarity*,  and  the  clipping 
off  of  the  half  waves  or  oscillations  due  to  this  phenomena,  causes  the  telephone 
receiver  to  have  a  pulsating  rectified  or  direct  current  (practically)  impressed  upon 
its  windings,  and  consequently  a  varying  or  constantly  changing  magnetic  pull  is 
exerted  upon  the  iron  diaphragm,  giving  rise  to  the  buzzes  heard  by  the  ear,  whenever 
a  wave  impinges  upon  the  aerial  circuit.  The  high  self-inductance  of  the  receiver 
coils  prevent  the  oscillations  from  passing  through  it,  instead  of  the  detector. 

Such  a  receiving  set  as  just  described,  is  not  capable  of  being  tuned  to  any 
desired  wave-length,  and  consequently,  except  for  certain  wave-lengths  or  short 
distance  work,  its  sphere  of  usefulness  is  quite  limited. 

The  first  method  applied  to  tune  the  receiving  apparatus  to  any  desired  wave- 
length, employed  a  simple  cylindrical  coil  of  insulated  wire,  made  up  of  several 
hundred  turns  or  convolutions,  each  turn  being  insulated  from  its  neighbor,  and  a 
sliding  contact  arranged  to  make  connection  with  any  desired  number  of  turns.  The 
connection  of  such  a  tuning  coil  is  depicted  in  fig.  2,  at  T,  which  is  the  coil  of  wire 
above  mentioned.  More  or  less  of -the  wire  can  thus  be  readily  inserted  in  series  with 
the  aerial,  thereby  changing  its  wave-length  to  a  high  or  low  value. 

This  method  is  not.  however,  very  efficient  for  reasons  to  be  subsequently 
explained,  and  is  not  used  any  more,  except  for  the  purpose  of  an  extra  tuning  induc- 
tance, or  "loading  coil"  in  the  atrial  lead,  where  long  wave-lengths  beyond  the 
range  of  the  regular  instruments  are  to  be  received. 

The  next  method  utilized  for  tuning  the  receiving  apparatus,  was  that  where 
the  free  end  of  the  tuning  coil  is  grounded  or  connected  to  earth,  as  shown  in  fig.  3. 
This  scheme  at  once  rendered  the  tuning  coil  something  more  than  a  mere  dead 


"See  hook  on  "Detectors"  of  this  Course. 


Copyright  1012  hy  E.  I.  Co. 


58 


WIRELESS  COURSE— LESSON  NO.  8 


resistance  coil  in  the  aerial  lead,  or  in  other  words,  it  now  became  a  transformer 
of  the  type  commercially  used  and  known  as  an  "auto-transformer"  or  mono-coil 
transformer,  meaning  one  whose  primary  and  secondary  coils  were  combined  into 
one  coil,  instead  of  the  two  separate  windings  employed  in  most  transformers. 

This  tuning  coil  transformer  action  is  a  very  important  one  now,  in  receiving 
sets,  and  is  made  good  use  of  in  administering  the  proper  voltage  and  current  to  certain 
classes  of  detectors,  some  of  which  require  a  stronger  voltage  than  others,  for 
their  proper  operation.  These  are  usually  referred  to  as  current  actuated  and  voltage 
actuated  detectors,  respectively. 

The  manner  of  varying  this  impressed  detector  voltage,  in  virtue  of  the  trans- 
forming action  occurring  in  the  three-lead  tuning  coil,  is  due  to  the  following 
reasons: — • 

When  the  oscillations  set  up  on  the  aerial  wire  pass  through  the  tuning  induc- 
tance coil  T,  it  causes  this  coil  to  become  surrounded  by  an  electro-magnetic  field 
of  force,  which  embraces  all  the  turns  of  wire  thereon.  Now,  if  the 'section  of  the  coil 
represented  by  P  in  fig.  3,  is  taken  as  the  primary  winding  of  the  auto-transformer, 


D  Jt 


Fig.  2  T=" 

and  the  turns  or  section  at  S,  at  the  secondary  winding,  then  the  voltage  of  the 
secondary  leads  to  the  detector  will  be,  as  the  ratio  existing  between  the  number 
of  primary  and  secondary  turns,  i.  €.,  if  the  primary  were  connected  across  100  turns 


Fig.  3 


of  the  coil,  and  the  secondary  leads  across  only  70  turn's,  then,  supposing  thaf 
one  volt  passed  through  the  primary  section/  only  seven-tenths  of  a  volt  would  be 
taken  off  through  the  secondary  leads. 


WIRELESS  COURSE— LESSON  NO.  8 


59 


Here  the  transforming  action  is  step-down,  but  it  can  also  be  made  step-up,  by 
simply  reversing  the  ratios  and  connections  of  the  primary  and  secondary  sections, 
as  depicted  at  ng.  4,  in  which  case  it  is  at  once  perceived  that  the  aerial  slider  is 
below  the  detector  slider,  and  consequently  there  are  more  turns  of  the  coil  embraced 
in  the  secondary  section  S,  than  in  the  primary  section  P.  Hence  the  secondary 
voltage  impressed  upon  the  detector,  would  be  greater  than  the  primary  voltage, 
or  if  the  primary  potential  was  one  volt  passing  through  fifty  turns  of  wire,  and 
the  secondary  section  took  in  one  hundred  turns  of  the  same  coil,  then  the  latter 
voltage  would  be  stepped-up  in  the  same  proportion,  or  two  to  one,  or  the  secondary 
potential  would  be  twice  one  volt  or  two  volts.  Of  course,  in  wireless  work,  the 
potentials  obtaining  in  me  tuning  coil  circuits  are  usually  very  small,  except  when  a 
high  powered  station  is  in  close  proximity  to  the  station  receiving. 


Fig.  4 


This  type  of  auto-transformer  is  used,  in  heavy  commercial  electric  work  to 
step-down  the  voltage  applied  to  the  windings  of  induction  motors  in  alternating 
current  circuits.  The  one-coil  transformer  is  also  often  employed  to  step-up  A.  C.  volt- 
ages for  various  purposes,  being  very  simple  and  more  efficient  than  two-coil  trans- 
formers for  certain  classes  of  work.  Auto-transformers  have  been  built  to  step-up 
five  hundred  volts  to  two  thousand  or  more. 

Thus  the  first  tuning  coil  was  found  to  be  more  perfectly  tuned,  as  regards 
the  open,  and  detector  or  closed  oscillating  circuits,  when  provided  with  two  movable 
contacts  or  sliders. 


Fig.  5 


A  cut  of  a  well  designed  double  slide  tuning  coil  or  auto-transformer  is  illus- 
trated by  fig.  5,  this  particular  coil  having  a  tuning  wave-length  capacity  of  700 
meters,  or  2,310  feet  about.  This  coil  then  would  give  a  station  having  an  aerial 
wave-length  of  50  meters,  a  total  wave-length  of  750  meters.  The  wave-length 
of  the  tuning  coil  is  found  by  multiplying  the  total  length  of  wire  on  it  in  meters 
by  the  factor  four. 


60 


WIRELESS   COURSE— LESSON   NO.  8 


The  receiving  station  employing  any  form  of  a  single  coil  tuning  inductance 
is  called  a  "close-coupled"  set.  In  the  past  few  years,  due  to  certain  peculiarities 
occurring  in  radio-communication,  such  as  static  and  interterence  currents,  the  two- 
coil  or  regular  type  of  transformer  has  been  widely  adopted,  which  seems  to  give 
the  greatest  clearness  and  sharpness  in  tuning,  as  it  is  possible  to  place  the  secondary 
coil  in  any  relative  position  to  the  primary  or  aerial  coil. 

This  type  of  receiving  set,  involving  the  use  of  a  two-coil  transformer,  is  termed 
professionally  a  "loose-coupled"  set,  as  there  is  no  metallic  electrical  connection 
existing  between  the  primary  and  secondary  circuits,  in  other  words,  the  coupling 
is  therefore  loose.  A  standard  form  of  a  receiving  "loose-coupler"  or  transformer 
is  illustrated  in  fig.  6,  the  instrument  shown  being  one  of  the  well  known  line,  built 
by  the  Electro  Importing  Company,  of  New  York  City.  It  has  a  wave-length  capacity 
of  eight  hundred  meters,  and  makes  possible  the  very  finest  and  closest  tuning,  the 
accuracy  being  within  one  per  cent,  or  less. 


Receiving  transformers  are  generally  made  with  a  primary  or  crater  aerial 
winding  of  a  comparatively  few  turns  of  large  copper  wire,  about  No.  18  to  20  B.  &  S- 
gauge,  and  an  inner  sliding  secondary  coil  having  many  turns  of  fine  copper  wire,  about 
No.  28  gauge,  the  idea  of  this  arrangement  being  to  give  a  good  step-up  ratio  between 
the  primary  and  secondary  windings,  and  consequently  in  their  voltages,  although  this 
ratio  can  be  varied  considerably  by  the  position  of  the  primary  or  secondary  sliders 
and  of  the  secondary  coil  itself. 

It  has  been  found,  that  to  be  the  most  efficient  for  wireless  work,  which  involves 
the  use  of  high  frequency  currents,  the  copper  wire  used  on  tuning  coils  or  tuning; 
transformers  should  have  the  lowest  possible  inherent  capacity.  Enameled  wire, 
which  has  a  very  high  inherent  capacity,  is  thus  unsuited  for  these  purposes,  and 
the  best  wire  is  bare  copper,  with  the  individual  convolutions  or  turns  spaced  a 


724. 


Fig.  7 

(.Courtesy    "Moderft    Electrics.") 


slight  distance  apart,  so  that  they  do  not  touch-  and  short-circuit  themselves.  All 
of  the  tuning  coils  and  tuning  transformers  built  by  the  Electro  Importing  Com-^ 
pany,  exhibit  this  feature,  which  is  important  where  any  lortg  distance  work  is  to  be 
attempted.  The  covering  on  the  wire  acts  as  part  of  a  condenser,  with  the  wire  as 
the  charging  electrode,  and  the  higher  the  inductivity  of  the  covering,  the  more 
pronounced  the  capacity  or  condenser  effect,  which  tends  to  choke  back  the  oscilla- 
tions. This  effect  is  also  very  noticeable  in  all  long  distance  electric  lines;  whether 
under  the  watet  or  soil  of  ift  the  air.. 


WIRELESS   COURSE— LESSON   NO.  8 


61 


The  connections  of  a  receiving  station,  employing  a  loose-coupler,  is  shown  by 
fig.  7.  In  this  diagram  are  also  depicted  a  variable  condenser,  a  fixed  condenser,  and 
a  potentiometer  anu  oattery  for  an  electrolytic  detector  or  other  cymoscope  requir- 
ing battery  current  to  actuate  it. 

The  action  of  the  loose-coupler  or  transformer  is  as  follows: — Referring  to 
fig  8,  the  incoming  oscillations  or  currents  surge  along  the  aerial,  into  the  primary 
winding  of  the  transformer  L  C,  and  cause  an  electro-magnetic  field  of  force  to  be 
set  up  around  it,  whose  lines  of  force  naturally  embrace  the  adjacent  secondary  coil 
of  many  turns  of  fine  wire,  and  induce  in  it  an  electro-motive  force  which  passes 
out  into  the  detector  circuit. 


-*--! — h-H^1*  Cy 


The  electro-motive  force  induced  in  the  secondary  winding  of  the  loose-coupler 
is  dependent  upon,  the  ratio  existing  between  the  number  of  primary  turns  and  num- 
ber of  secondary  turns,  i.  e.,  if  the  sliders  of  the  primary  coil  are  set  to  include  20 
turns  of  wire,  and  the  secondary  turns  in  use  amount  to  100,  then  the  "ratio  of 
transformation,"  existing  between  the  two  coils  is  as  100:20  or  5  to  1,  and  the 
secondary  voltage  would  be  equivalent  to  five  times  the  primary  voltage,  the  current, 
however,  being  decreased  accordingly,  as  the  total  energy  cannot  be  increased,  only 
changed  in  its  form.  So  if  one-tenth  of  an  ampere  at  one  volt  pressure  was  the 
primary  energy  passing,  and  the  ratio  of  transformation  equalled  to  5  to  1,  then 
the  secondary  energy  would  be  in  the  form  of  5  volts,  and  but  one-fifth  of  the  current 
or  one-fifth  of  one-tenth  ampere,  which  is  one-fiftieth  of  an  ampere.  This  supposes 
that  the  efficiency  of  transformation  is  100  per  cent.,  but  for  an  air-core  transformer 
of  this  type,  the  efficiency  would  be  very  much  below  this  figure,  probably  not  above 
5  per  cent.  Thus  the  secondary  voltage  is  equal  to  the  calculated  value  as  stated 
above,  but  due  to  the  losses  in  transformation  the  current  strength  is  about  5  per 
cent,  of  the  computed  value,  or  5  per  cent,  of  1-50  ampere,  which  is  1-1,000  ampere. 
These  figures  are  taken  merely  to  help  explain  the"  action  taking  place,  and  are  of 
course  much  smaller  in  actual  wireless  work,  the  current  strength  being  about  40 
micro-amperes  or  40  millionths  of  an  ampere,  when  good  readable  signals  are 
received  with  a  crystal  rectifying  detector,  such  as  the  Perikon. 

The  reason  why  this  class  of  apparatus,  whether  one  or  two-coil  type,  realizes 
such  a  poor  efficiency  is  because  the  electro-magnetic  lines  of  force  must  be  carried 
through  the  air.  instead  of  iron,  which  has  an  electro-magnetic  conducting  power 
varying  from  100  or  more,  times  that  of  air.  resultant  in  only  a  fraction  of  the 
magnetic  flux  of  the  primary  coil  reaching  the  secondary  coil. 


62 


WIRELESS   COURSE— LESSON   NO.  8 


Recently,  electrical  scientists,  have  bestirred  themselves  with  the  idea  of  placing 
a  properly  designed  iron  core  in  wireless  oscillation  transformers,  and  by  no  less 
an  aunionty  than  Dr  Charles  P.  Steinmetz,  Chief  Electrical  Engineer  for  the  General 
Electric  Company,  of  America.*  The  use  of  iron  for  such  high  frequency  currents 
as  encountered  in  wireless  apparatus,  varying  from  a  few  hundred  thousand  cycles 
up  to  a  million  or  more  per  second,  would  bring  out  some  new  and  unknown  results 
undoubtedly,  tending  to  the  more  efficient  operation  of  such  apparatus  quite  likely. 

Up  to  this  time,  no  iron  has  been  utilized  in  oscillation  transformers,  either 
transmitting  or  receiving,  owing  to  the  excessive  time  lag  incurred  by  the  iron  mass 
in  having  to  so  rapidly  change  its  magnetic  polarity,  the  molecules  of  which  it  is 
'composed  being  obliged  to  turn  over,  end  for  end,  according  to  the  theory  now 
held,  and  the  friction  occurring  between  the  millions  of  molecules,  whenever  the 
magnetism  reverses,  is  quickly  manifested,  as  soon  as  the  frequency  of  reversal  exceeds 
20  to  30  cycles  per  second. 

If  iron  is  introduced  for  this  purpose,  it  will  undoubtedly  have  to  be  a  specially 
prepared  grade,  and  extremely  soft  and  homogenous,  besides  being  divided  up  into 
very  fine  sections. 

Besides  the  familiar  tuning  coil  and  loose-coupler  for  receiving  purposes,  there 
is  another  instrument  known  as  a  "variometer,"  which  is  employed  extensively  'by  the 
Tclefunken  Wireless  Company.  This  instrument  is  nothing  more  than  two  helices 
of  wire,  one  within  the  other,  the  inner  helix  being  .adjustable  as  regards  its  position 
in  relation  to  the  other  helix. 


Fig.  9 


In  fig.  9,  is  shown  the  idea  of  the  variometer,  H  2  being  the  outer  helix,  and 
H  1  the  inner  rotative  helix.  Change  in  wave-length  is  accomplished  in  this  instru- 
ment, by  rotating  the  movable  inner  coil  or  helix,  to  have  a  certain  position  in  respect 
to  the  stationary  helix,  this  position  determining  the  value  of  the  self-inductance 
and  mutual  inductance  of  the  two  coils.  Usually  it  is  utilized  in  conjunction  with 
a  variable  capacity  or  condenser,  as  then  it  becomes  possible  to  tune  quite  sharply. 
The  variable  capacity  is  generally  shunted  across  one  of  the  variometer  coils. 

Before  taking  up  the  next  section,  on  receiving  apparatus,  a  few  paragraphs' 
will  be  devoted  to  a  remarkable  receiving  instrument  devised  and  perfected  by 'Hugo 
Gernsback,  of  New  York  City. 

It  is  patented  by  Hugo  Gernsback  and  is  very  well  adapted  to  the  requirements 
of  all  portable  wireless  stations,  such  as  those  in  mule  pack  sets,  aeroplane  and 
airship  sets,  and  in  a  hundred  other  places,  where  light  weight  and  great  compact- 
ness are  prime  requisites. 


*See  Dec..  1911,  Proceedings  American  Institute  of  Electrical  Engineers, 


WIRELESS   COURSE— LESSON   NO.  8 


63 


A  view  of  the  instrument,  which  is  called  by  its  inventor  a  "Detectorium," 
is  shown  at  fig.  10.  The  Detectorium  combines  a  tuning  coil,  of  the  double  slide 
type,  and  a  crystal  rectifying  detector,  such  as  the  silicon,  in  one  compact  instru- 
ment, which  weighs  but  18  ounces,  or  with  a  pair  of  head  receivers  and  some 
aluminum  aerial  wire,  the  whole  outfit  will  not  weigh  more  than  2^2  pounds. 


Fig,  10 


The  unique  part  of  the  instrument  lies  in  the  detector  arrangement,  which  makes 
use  of  a  piece  of  silicon  or  other  crystal,  fastened  onto  a  spring  protruding  from 
one  of  the  tuner  sliders,  and  by  using  this  crystal  as  a  contact  point,  rubbing  against 
the  bared  convolutions  of  the  coil,  the  inventor  makes  it  possible  to  actually  tune 
with  a  detector.  The  instrument  was  thoroughly  tried  out  and  proved  very  sensitive 
and  positive  in  its  action. 

In  the  drawing  fig.  11,  are  shown  the  best  methods  of  connecting  up  the  instru- 
ment, the  arrangement  at  C,  having  been  found  to  be  about  the  best,  especially 
where  there  is  much  static  or  interference  to  cut  out. 


(Courtesy   "Modern    Electrics.") 


A  portable  receiving  set  comprising  a  high  antenna,  1, 200-meter  tuning  coil,  silicon 
detector,  variable  condenser,  receivers,  testing  buzzer,  battery  and  ground  connection, 
is  shown  below,  and  was  fully  described  in  "Modern  Electrics." 

The  antenna  for  this  outfit  consists  of  a  single  No.  28  wire  which  is  elevated  by 
means  of  a  four-foot  "tailless"  kite,  being  either  dropped  down  perpendicularly  from 
the  kite  or  run  parallel  with  the  kite  string.  A  spring  clip  on  the  end  of  a  flexible 
cord  makes  connection  with  the  antenna  wire.  The  wire  is  made  very  light  and  cov- 
ered with  cloth.  It  is  rendered  portable  by  making  the  curved  cross  stick  removable. 
As  this  set  is  used  in  all  kinds  of  weather,  three  different  weights  of  string  (seine- 
twine)  are  used. 

A  magneto  telephone  box  with  inside  dimensions  of  7x4^4x4  inches,  contains  the 
detector,  condenser,  tuning  coil,  buzzer  and  its  battery. 

The  tuner  has  a  2]4  inch  core  7  inches  long  wound  with  75  meters  of  No.  28 
bare  wire.  In  with  this  is  a  loading  coil  containing  225  meters  of  No.  32  wire  which 
is  "tapped'*  at  intervals  of  75  meters,  taps  leading  to  a  four-point  switch.  This 
method  ^of  using  a  loading  coil  js  the  only  way  by  which  so  long  a  wave  length  may 
be  obtained  within  such  a  limited  space.  To  our  definite  knowledge  this  plan  has 
never  been  used  before,  at  least  has  not  come  to  our  notice. 


64 


WIRELESS   COURSE— LESSON   NO.  8 


The  detector  is  held -inside  the  box  by  a  spring  fastener  when  not  in  use,  and 
when  in  use  is  connected  to  binding  posts  on  the  outside  of  box.  The  silicon  detector 
is  chosen  as  being  least  liable  to  injury  or  getting  out  of  adjustment,  besides  ranking 
close  to  the  electrolytic  in  sensitivity. 


Fig.  12 


(Courtesy  "Modern  Electric*?.") 


The  variable  condenser  is  capable  of  fairly  close  regulation  and  may  be  made 
of  any  convenient  size.  The  condenser  is  rolled  up  into  a  cylinder  and  fastened 
to  the  inside  of  the  box  cover  with  the  condenser  switch  on  the  outside  of  the  'box. 

The  testing  buzzer,  which  is  almost  indispensable,  is  a  very  small  one,  and  is 
connected  through  a  flush  type  push  button  to  a  small  flash  light  battery,  fastened 
also,  on  the  inside  of  the  cover. 

The  ground  consists  of  an  iron  rod  about  18  inches  long,  with  a  ring  in  the  end 
to  facilitate  pushing  in,  and  especially  pulling  out  of  ground. 

The  ground  and  antenna  are  connected  through  flexible  cords  to  binding  posts  on 
the  outside  of  box. 

Double  head  receivers  are  almost  a  necessity,  as  little  can  be  heard  without  them 
on  account  of  wind,  etc. 


Fig.  13  Fig.   14 

(Courtesy  "Modern  Electrics.") 

Fig.  12  shows  the  connections  used,  while  figs.  13  and  14  are  photos  of  the  outfit 
packed  and  unpacked. 

This  set  has  actually  been  unpacked,  set  up,  and  receiving  messages  inside  of  five 
minutes.  It  is  capable  of  fine  tuning  and  excellent  results  have  been  obtained  with  it. 

In  case  of  damage  to  the  kite,  or  when  there  is  no  wind,  fairly  good  results  may 
be  obtained  by  attaching  a  stone  to  the  wire  and  throwing  it  over  a  high  tree  or  barn. 

(To  be  continued  Next  Lesson) 


WIRELESS  COURSE—  LESSON  NO.  9 


65 


Lesson  Number  Nine 


RECEIVING  APPARATA,  CONCLUSION. 
PART  TWO. 

HE   commonest   type   of   receiving  set  and  an   explanation   of  the   tuning  trans- 
formers  employed  were  covered  in  the  preceding  book.     In  the  present  paper, 
the  function  of  the  condensers,  head  receivers  and  potentiometers  will  be  dis- 
cussed,  the    detectors   receiving   exhaustive    treatment    in    a    special    book. 

To  begin  with,  a  diagram  for  the  connecting  up  of  the  above  named  instru- 
ments is  referred  to  at  fig.  1,  wherein  A  is  the  aerial,  T  the  loose-coupler,  V  C 
a  variable  condenser  or  capacity,  D  an  electrolytic  detector  requiring  battery  current 
to  actuate  it,  R  head  telephone  receivers,  P  adjustable  resistance  or  a  potentiometer 
shunted  across  the  battery  terminals. 

The  variable  condenser  may  be  used  in  a  number  of  different  ways,  a  small  one 
sometimes  being  connected  across  the  secondary  coil  of  the  loose-coupler.  For 
further  diagrams  of  proper  connections  of  the  various  apparatus,  the  student  is 
referred  to  the  lesson  on  "Hooks-Ups  and  Connections,"  where  every  standard  send- 
ing and  receiving  connecting  scheme  is  given  in  full. 


Fig.  1 


(Courtesy  "Modern  Electrics.") 


The  variable  capacity  in  the  primary  circuit  makes  it  possible  to  vary  the  wave- 
length, as  this  is  dependent  upon  the  oscillation  constant,  which  is  the  square  root 
of  the  product  of  the  inductance  and  the  capacity.  Hence,  sharper  tuning  and 
better  elimination  of  stray  currents  incurred  by  static  and  interference  is  possible. 
For  long  wave-lengths,  the  variable  condenser  should  shunt  the  inductance  or 
primary  coil  as  shown  in  fig.  1,  but  for  tuning  in  short  wave-lengths  the  capacity 
must  be  connected  in  series  with  the  ground  wire,  or  between  the  primary  winding 
and  the  ground  connection. 

Variable  condensers  are  constructed  in  several  ways,  the  standard  commercial 
pattern  having  two  sets  of  semicircular  metal  plates,  with  a  small  air  space  separating 
each  of  the  plates  from  its  neighbor.  One  of  the  sets  Js  made  stationary  while 
the  other  set  is  mounted  upon  a  movable  spindle,  permitting  the  rotating  of  it  and 
the  attached  plates,  so  that  more  or  less  of  their  surface  may  be  inserted  between 
the  stationary  plates,  with  a  consequent  increase  in  the  capacity,  or  vice  versa. 

The  maximum  capacity  is  obtained  when  the  moving  plates  are  totally  within  the 
stationary  plate  air  spaces,  and  the  minimum  capacity,  when  the  moving  plates 
are  entirely  removed  from  the  stationary  plate  air  spaces.  This  form  of  condenser 
was  originally  devised  by  Kordia,  and  so  it  is  called  the  Kordia  air  condenser. 

In  so.ne  condensers  of  this  type,  the  precision  of  adjustment  has  been  so  close 
that,  only  1-100  inch  separated  the  moving  plates-  and  stationary  ones.  If  the 
plates  toacn  at  any  point,  the  condenser  would  at  once  be  rendered  useless,  or 
in  other  \\ords,  it  would  be  short-circuited  and  cut  out  of  circuit. 

At  fig.  2,  is  shown  the  construction  of  a  rotary  plate  condenser,  for  receiving 
circuits. 

A  cut  of  a  sliding  plate  variable  condenser,  built  by  the  Electro  Importing  Com- 
pany, is  illustrated  at  fig.  3.  This  condenser  admits  of  varying  the  capacity  from 
zero  to  maximum,  by  simply  pushing  the  moving  plates  in  between  the  fixed  ones, 
and  from  maximum  to  zero,  by  withdrawing  them  from  the  fixed  plates.  This  type  of 
condenser  originated  by  H.  Gernsback  in  1907. 

The  condenser  illustrated  here,  has  17  plates  of  aluminum  in  all.  9  of  them 
being  fixed  or  stationary  and  8  of  them  moving,  the  individual  plates  being  separated 
by  a  minute  air-gap.  This  condenser  has  a  maximum  capacity  with  the  moving  plates 
all  the  way  in,  of  .0016  microfarad,  which  is  sufficiently  high  for  most  any  requirements. 
Ordinary  rotary  plate  air  condensers  have  about  .001  microfarad  capacity. 

The  capacity  of  an  air  dielectric  (insulated)  condenser  such  as  these,  is  directly 
dependent  upon  the  total  active  area  of  air,  which  is  surrounded  by  condenser  plates 
of  opposite  polarity;  the  thickness  of  the  air  space  between  the  plates;  the  induc- 
tivity  factor,  which  for  air  at  ordinary  pressure  is  1. 

Copyright  1912  by  E.  I.  Co. 


66 


WIRELESS  COURSE— LESSON  NO.  9 


This  being  so,  it  becomes  a  simple  matter  to  compute  the  capacity  of  a  certain 
condenser,  if  the  total  area  of  active  air  space,  between  the  plates  is  known,  and 
also  the  specific  capacity  per  one  unit  of  area. 

For  example,  the  specific  capacity  in  microfarads  for  one  square  inch  of  air  at 
ordinary  pressure  (14.7  pounds  per  square  inch,  or  atmospheric  pressure)  and  1-16 
of  an  inch  thick,  is  .OC0003596  M.  F.  For  a  similar  area,  only  1-32  of  an  inch  thick, 
the  capacity  would  be  double  that  given  for  the  1-16  inch  air  gap.  In  other  words, 
the  closer  the  condenser  plates  of  opposite  polarity  are  brought,  the  greater  the 
capacity  obtained,  other  things  being  equal,  but  the  plates  must  not  approach  so 
close  to  each  other,  that  the  potential  can  break  down  the  condenser,  by  jumping 
between  them. 


?///////  ///////////////  //A 


Fig.  2 

fl-  Glass  C<z.sin<f 
B~  /nj  &<l<x.  f/flpiJ&jO 
C-  Conp*r  burrs 

O  - 
£  • 


(Courtesy   "Modern    Electrics.") 

Knowing  the  capacity  per  square  inch  of  active  dielectric,  then  it  is  only  neces- 
sary to  multiply  the  total  number  of  square  inches  of  active  air  in  tlte  whole  con- 
denser by  it,  and  the  result  will  be  the  maximum  capacity  in  microfarads. 

As  an  example:  suppose  a  rotary  air  condenser  has  21  stationary  semi-circular 
plates,  and  20  moving  plates  of  similar  shape,  the  diameter  of  the  plates  being  6 
inches.  The  air  space  between  the  stationary  and  moving  plates  is  1-16  inch.  First, 
it  is  necessary  to  ascertain  the  area  of  one  moving  plate,  which  is  that  of  half  a 
circle,  with  a  diameter  equal  to  that  of  the  plate.  The  area  in  square  inches  is 
found  by  the  formula: — 


A      ^Xr2 
A=—       -  or 


TT 

4  X  d  - 


2  2 

Where:  A  is  the  area  in  sq.   in.  of  one-half  a   circle. 

TT  is  3.1416   (a  constant). 

r  is   the   radius  in  inches    (one-half  the   diameter). 

d   is   the   diameter   in  inches. 

Hence,  applying  this  rule  to  the  above  problem,  it  is  ascertained  that  the  area 
of  one  moving  plate  is  14.1372  sq.  in.  Now,  each  moving  plate  is  surrounded  on  both 
sides  by  a  stationary  charging  plate,  so  that  the  total  active  air  space  exposed  to 
charge,  is  twice  the  number  of  moving  plates  or  20  times  2,  or  40  air  spaces,  and 
the  total  active  air  area  in  sq.  in.  must  be  40  times  14.1372  sq.  in.  or  565.488  sq.  in. 
The  maximum  capacity  is  then,  565.888  times  the  capacity  per  one  sq.  in.  of  air 
1-16  inch  thick  (.000003596  M.  F.),  or  .002033  +  M.  F. 


WIRELESS  COURSE— LESSON  NO.  9 


67 


Some  types  of  variable  condensers  employ  other  dielectric  than  air,  which  greatly 
increases  the  resultant  capacity,  as  the  charging  plates  or  surfaces  can  be  brought 
very  much  closer  together. 


Fig.  3 


Fig.   4 


An  entirely  new  style  of  Variable  Condenser  giving  an  enormous  capacity  in  a 
comparatively  small  space  is  known  as  the  "Gernsback"  Rotary  Variable  Condenser, 
after  its  inventor,  and  is  the  first  condenser  using  this  principle. 

From  the  illustrations,  it  will  be  seen  that  a  central  roll  operating  much  the  same 
like  a  roller  shade  winds  and  unwinds  flexible  insulating  sheets  between  thin  metallic 
sheets. 

There  are  three  rolls  altogether  and  the  actual  condenser  is  wound  on  the  central 
roll.  Thus  a  very  high  capacity  is  obtained  simply  by  moving  the  central  knob  back 
and  forward.  The  capacity  is  .01  Microfarad,  an  astonishing  capacity  for  so  small  a 
condenser. 

The  adjustment  of  the  capacity  from  zero  to  maximum  is  easily  accomplished 
by  turning  the  knob  on  the  end  of  the  cabinet.  One  very  agreeable  feature  possessed 
by  this  condenser  over  other  variable  condensers,  is  that  it  can  be  used  laying  flat 
on  the  table,  enabling  the  operator  to  adjust  it,  without  having  to  raise  his  arm 
and  hand,  a  foot  or  so  in  the  air  to  reach  the  knob,  as  is  the  case  with  vertical 
types.  Also  there  is  no  possibility  of  the  opposite  charging  leaves  becoming  short- 
circuited,  as  often  occurs  in  the  regular  inter-leaving  plate  types.  The  charging 
surfaces  are  separated  by  a  special  dielectric,  only  one  thousandths  inch  thick,  which 
gives,  of  course,  a  remarkable  capacity  to  the  condenser,  and  amply  sufficient  for  any 
needs  arising  in  the  reception  of  wireless  messages. 


INTERIOR    OF    GERNSBACK    VARIABLE    CONDENSER. 

(Courtesy   "Modern   Electrics.") 

There  are  and  have  been  a  number  of  different  types  of  variable  condensers 
used,  besides  those  so  far  mentioned,  but  this  subject  will  end  with  a  mention  of  the 
"Tubular"  type,  which  is  much  in  favor  with  the  Marconi  Company. 

The  tubular  variable  capacity,  consists  of  two  or  more  metal  tubes,  usually 
brass,  having  walls  about  1-16  inch  thick,  arranged  so  that  one  of  the  tubes,  or  a  set 
of  them,  can  be  pushed  within  the  other  tube,  or  set  of  tubes,  leaving  a  small  air 
space  between  them.  Sometimes  the  inner  tube  has  a  piece  of  insulating  material, 
such  as  hard  rubber  or  oiled  linen  (Empire  cloth),  secured  around  it,  permitting 
the  tubes  to  be  quite  close  to  each  other,  yet  not  touching.  This  makes  a  very  good 
condenser,  the  capacity  of  which  depends  upon  the  diameter,  length  of  the  tubes,  and 
their  number;  and  also  upon  the  thickness  of  the  air  space  left  between  them. 

In  the  realm  of  receiving  condensers,  the  other  form  much  used  in  wireless 
work,  is  the  fixed  or  stationary  type,  whose  capacity  is  not  adjustable,  except  in  steps 
n  some  makes.  The  fixed  condenser  is  employed  in  practically  all  wireless  receiv- 
ing sets  to-day,  for  the  purpose  of  intensifying  the  effect  of  the  high  frequency 


68 


WIRELESS  COURSE— LESSON  NO.  9 


oscillations  upon  the  detector,  by  virtue  of  its  constant  charging  and  discharging. 
It  is  sometimes  found  that,  if  the  telephone  receivers  are  connected  across  the  fixed 
condenser,  where  crystal  rectifying  detectors  are  employed,  the  received  signals  are 
louder  and  stronger,  than  if  they  are  connected  across  the  detector,  but  this  depends 
upon  the  capacity  of  the  condenser  and  several  other  factors. 

The  fixed  condenser  is  sometimes  shunted  around  the  detector,  i.  e.,  connected 
across  its  terminals. 

A  typical  fixed  condenser  of  the  series-parallel  »form,  is  shown  in  fig.  5.  This 
and  the  small  fixed  condenser  of  the  multiple  type  at  fig.  6,  are  manufactured  by 
the  Electro  Importing  Company. 

The  condenser  depicted  by  fig.  5,  is  composed  of  two  distinct  units  connected 
to  three  terminal  posts,  so  that  it  is  possible  to  connect  either  one  of  the  units 
into  circuit:  both  of  them  on  parallel  or  both  in  series,  the  latter  connection  having 
been  found  to  give  the  best  results  generally,  as  the  discharge  voltage  of  the  two 
units  in  series  is  the  highest  of  any  combination,  and  very  desirable  where  voltage 
operated  detectors  are  utilized.  This  condenser  is  constructed  of  alternate  sheets 
of  metal  foil,  interleaved  between  slightly  larger  sheets  of  extra  thin  dielectric, 
resulting  in  a  very  high  capacity. 

The  smaller  fixed  condenser,  illustrated  at  fig.  6,  is  of  very  neat  and  efficient 
construction,  and  has  a  capacity  of  .0165  microfarad. 


Fig.  5 


Fig.  6 


For  a  number  of  cymoscopes  or  detectors,  it  is  necessary  to  have  a  means  of 
applying  a  critical  electro-motive  force  or  voltage  to  them,  the  energy  usually  being 
supplied  by  dry  or  storage  cells.  The  applied  voltage  must  be  susceptible  of  being 
varied  very  gradually  from  weak  to  strong  and  vice  versa.  Besides  this  feature,  the 
method  of  controlling  the  voltage  and  current  must  be  such,  that,  any  desired  fraction 
of  the  voltage  can  be  used  on  the  detector,  without  simultaneously  changing  the 
current  value,  which  occurs  where  ordinary  resistance  is  inserted  in  series  with  the 
source  of  energy  and  the  device  taking  the  current. 

This  principle,  known  as  the  potentiometer  or  bridge  method,  is  shown  better 
by  the  diagram  at  fig.  7.  Here  a  battery  B,  of  say  6  volts  potential,  passes  a  current 
through  the  potentiometer  or  shunt  resistance  P,  made  up  of  100  turns  of  resistance 


Fig.  7 


wire.  Connected  to  one  side  of  the  potentiometer  resistance  is  the  telephone 
receivers  R,  and  detector  D,  and  the  other  lead  from  the  detector  terminating  in  a 
slider  or  movable  contact,  at  S,  which  permits  of  the  detector  being  shunted  across 
any  number  of  turns  of  resistance  wire. 


WIRELESS  COURSE— LESSON  NO.  9 


69 


The  action  is  as  follows: — If  6  volts  is  passing  through  the  100  turns  of  resistance 
wire,  then  the  voltage  impressed  upon  the  detector  circuit,  is  directly  proportionate 
to  the  number  of  turns  embraced  by  its  slider  S,  and  other  fixed  connection.  If  the 
slider  is  set  to  embrace  all  the  turns  of  wire,  the  voltage  applied  to  the  detector 
circuit,  will  equal  that  of  the  battery,  viz.,  6  volts;  but-  if  the  slider  is  set  at  say 
50  turns,  from  the  end  of  the  coil,  then  only  SO-lOOths  or  one-half  of  the  battery 
potential,  3  volts,  will  operate  on  the  detector  circuit. 

At  one  time,  potentiometers  of  the  resistance  coil  type,  were  widely  used,  but 
it  soon  became  evident  that  they  could  not  be  effectively  used  for  this  purpose,  as 
the  inductive  kick  due  to  the  self-inductance  of  the  coil  of  wire,  caused  noises  in 
the  telephone  receivers,  which  greatly  interfered  with  the  reception  of  messages, 
so  the  only  remedy  for  this  state  of  affairs,  was  to  utilize  a  non-inductive  potentio- 
meter, and  to-day  this  is  a  cardinal  feature  of  all  potentiometers  intended  for  wire- 
less work. 

One  of  the  first  and  best  non-inductive  potentiometers  introduced  on  the  market, 
was  that  making  use  of  a  carbon  or  graphite  rod  of  high  resistance,  mounted  on  an 
insulating  base,  and  having  a  rolling  wheel  or  ball  contact  traveling  along  its 
length,  by  which  means  it  was  possible  to  cut  in  any  desired  amount  of  resistance, 
within  the  limits  of  the  instrument.  The  total  resistance  of  the  carbon  rod  is  300 
ohms.  This  instrument,  which  has  been  extensively  adopted  in  all  wireless  receiving 
stations  is  illustrated  at  fig.  8. 

In  a  later  type  of  this  potentiometer,  the  adjustment  of  the  resistance  has  been 
perfected,  so  that  it  is  accomplished  by  a  turn  of  a  rotary  knob,  with  a  pointer 
or  index  attached,  to  indicate  the  degree  of  resistance  in  circuit.  This  instrument 
appears  at  fig.  9.  It  is  also  non-inductive,  and  very  easy  of  adjustment,  taking  up 
premium.  Both  these  instruments  originated  with  H.  Gernsback  and  are  patented  by 
him. 


Fig.    8 


Fig.    9 


The  most  important  instrument,  aside  from  the  detector  itself,  is  the  telephone 
receiver,  serving  to  make  intelligible  to  the  human  ear,  the  various  changes  going 
on  in  the  detector  circuit,  whenever  an  incoming  oscillation  representing  a  signal 
impinges  upon  it.  The  changes  occurring  in  the  detector  circuit,  due  to  the  action 
of  the  detector  under  the  influence  of  an  oscillatory  high  frequency  current,  are 
infinitesimally  small  and  minute,  and  naturally  an  instrument  which  is  capable  of 
detecting  and  interpreting  them,  must  of  necessity  be  extremely  sensitive. 

For  the  purpose  of  receiving  signals  over  very  short  distances,  it  is  possible 
to  use  a  common  low  resistance  telephone  receiver,  having  a  small  number  of  turns  of 
wire  upon  its  bobbins,  but  for  serious  work  over  a  greater  distance  than  10  miles,  it  is 
necessary  to  employ  special  wireless  receivers,  wound  with  many  hundred  turns 
of  fine  copper  wire,  and  equipped  with  good  strong  permanent  magnets  of  the  best 
grade  of  steel,  such  as  Tungsten  or  Swedish  steel,  coupled  with  a  thin  soft  iron 
diaphragm  of  proper  thickness,  the  air  gap  left  between  the  magnet  pole-faces  and  it, 
being  very  short  and  correctly  adjusted. 

A  cut  of  a  pair  of  head  receivers  widely  adopted  by  commercial  and  experi- 
mental stations,  is  shown  at  fig.  10.  These  receivers  are  supplied  by  the  Electro 
Importing  Company,  and  they  guarantee  them  to  respond  to  the  following  wonderful 
-If  the  nickel  cord  tips  are  slightly  moistened  and  then  touched  by  the 
ringers,  the  receivers  will  respond  by  emitting  a  noise,  very  minute  of  course,  but 
showing  that  an  electric  current  has  been  set  up  and  passed  through  the  receiver 
magnet  coils,  which  although  in  the  magnitude  of  one  one-hundred-thousandth  of 


70 


WIRELESS   COURSE— LESSON   NO.  9 


a  volt,  and  one  one-millionth  of  an  ampere,  has  been  made  audible  to  the  ear  by 
a  click  of  the  diaphragm.  Surely  a  remarkable  demonstration  of  the  sensitiveness 
of  the  receivers,  in  fact  there  is  possibly,  not  at  the  present  time,  a  more  susceptible 
electrical  device  obtainable  than  a  high  resistance  wireless  receiver,  such  as  these. 
The  sensitiveness  of  a  wireless  receiver  depends  upon  the  correct  proportioning 
of  its  various  parts;  the  proper  strength  of  its  permanent  magnets,  and  the  number 


Fig.  10 


of  turns  of  copper  wire  wound  upon  its  magnet  spools,  not  upon  how  many  megohms 
of  resistance  that  can  be  crowded  into  it.  If  this  were  the  case,  German  silver 
or  other  high  resistance  wire  might  as  well  be  used  on  the  bobbins. 

The  idea  is,  to  get  the  greatest  possible  number  of  ampere  turns  active  on  the 
receiver  magnet  spools,  which  determines  the  effect  of  a  certain  current  strength 
upon  the  diaphragm.  By  ampere-turns  is  inferred  the  product  of  the  amperes  passing 
through  a  coil  and  the  number  of  turns  of  wire  thereon,  this  determining  directly 
the  amount  of  magnetic  flux,  in  lines  of  force  per  square  unit  of  cross-section, 
which  will  be  set  up  to  react  upon  the  diaphragm. 

The  best  receivers  now,  are  wound  with  No.  50  B.  &  S.  gauge  or  finer  silk 
covered  wire,  of  the  very  best  annealed  copper.  The  resistance  in  ohms  of  the  best 


Fig.  11 


types  does  not  exceed  1,600  to  2,000  ohms  per  receiver  of  3,200  to  4,000  for  a  pair. 
Formerly  there  were  some  receivers  made  having  a  resistance  per  set  of  6,000 
ohms  and  more,  but  this  is  higher  than  is  usually  necessary. 


WIRELESS  COURSE— LESSON  NO.  9 


71 


A  cut  of  a  pair  of  extra  fine  professional  type  receivers  are  illustrated  by  fig.  11. 
These  are  the  Electro  Importing  Company's  very  best  make,  and  are  hand  made, 
in  the  laboratory. 

Although  not  generally  known,  it  is  essential  for  the  best  results,  that  the  two 
receivers  of  a  set  shall  have  the  same  tone,  as  it  is  called,  and  the  best  receivers, 
such  as  those  shown  above,  are  mated  up  into  pairs  in  this  manner.  The  usual 
custom  is  to  connect  the  two  receivers  of  a  set  in  series,  and  it  may  be  said  in  this 
connection,  that  it  has  been  found  very  unsatisfactory  to  connect  a  pair  of  receivers 
having  different  resistances,  such  as  1,000  and  75  ohms,  together. 


Fig  12. 

At  fig.  12,  is  shown  a  cut  of  a  75  ohm  receiver,  suitable  for  experimental  work, 
and  short  distance  wireless  reception  of  signals.  This  receiver  is  of  good  con- 
struction and  quite  light  in  weight. 


Fig.  13 

Fig.  13,  shows  a  receiving  set  built  by  the  A.  E.  G.,  Berlin,  and  extensively  used 
in  large  commercial  stations,  including  the  U.  S.  Navy.  This  set  employs  a  coherer 
and  tape  recorder,  so  that  a  record  of  the  messages  can  be  taken  automatically. 


72 


WIRELESS  COURSE— LESSON   NO.  9 


1 


l_._ 


MORSE  | 

•LmiL  I      il • • 


Fig.  14  illustrates  the  diagram  of  the  connections  for  this  receiving  set,  including 
the   relay,   coherer  and   decoherer,   condensers,  and  polarization   cells. 


Fig.  15 


In  Fig.  15,  is  depicted  the  same  set,  with  lid  raised  to  show  the  wiring  and  connec- 
tion of  the  various  apparatus. 


WIRELESS  COURSE— LESSON  NO.  10 


Lesson  Number  Ten. 


THE  DETECTORS. 

SHE  most  vital  instrument  in  the  receiving  set  is  the  detector,  though  this  instru- 
ment is  largely  dependent  on  the  efficiency  of  the  telephone  receiver  for  the 
results. 

The  student  will  recall  that  we  have  stated  in  previous  lessons  the  fact  that 
energy  radiated  from  wireless  transmitting  instruments  is  in  the  form  of  alternating 
current  of  extremely  high  frequency.  Now,  the  student  will  logically  suppose  that 
an  instrument  could  be  inserted  in  the  aerial  circuit  between  the  aerial  and  the 
ground,  and  that  the  current  would  operate  this  instrument  so  that  an  indication 
of  passing  current  could  be  obtained.  But,  a  galvanometer  cannot  be  mad£  to  indi- 
cate such  high  frequency  current  since  the  pointer  would  have  to  move  with  the 
same  rapidity  as  the  periodic  changes  in  the  oscillations,  and  the  results  would  be 
that  the  moving  parts  in  the  galvanometer  would  remain  stationary,  being  unable 
to  follow  the  rapid  motion.  The  same  results  apply  to  the  telephone  receiver,  since 
the  diaphragm  cannot  follow  the  rapid  alternations  of  the  received  energy.  Fur- 
thermore, in  the  case  of  a  telephone  receiver,  on  account  of  the  large  self-induction 
of  the  instrument,  the  high  frequency  voltage  generated  by  the  waves  would  pro- 
duce in  a  circuit  containing  a  telephone  receiver  only  extremely  weak  currents.  It 
is  therefore  obvious  that  an  instrument  must  be  resorted  to,  in  order  to  transform 
this  high  frequency  current  so  as  to  make  it  operative  on  the  telephone  receiver. 

Such  an  instrument  is  known  as  a  detector,  and  the  various  types  of  these  detec- 
tors operating  on  a  different  principle  are  classified  as  follows: — 

Coherers;  Magnetic;  Thermal;  Crystal  Rectifiers;  Electrolytic;  and  Vacuum 
detectors. 

We  will  first  consider  the  coherer  type,  which  has  already  been  described  in  an 
earlier  lesson.  The  coherer  exists  in  various  forms,  the  most  widely  known  form 
being  the  filings  coherer,  originally  employed  by  Marconi.  Such  a  coherer  is  no 
longer  employed  commercially,  and  is  only  used  to  demonstrate  the  principles  of 
wireless  telegraphy  to  an  audience.  This  detector  is  extremely  unreliable,  and 
must  be  continuously  adjusted.  If  a  loud  signal  is  suddenly  received  by  the  coherer, 
it  will  cause  it  to  "jam,"  by  which  is  meant  that  the  fine  filings  will  become  burnt 
and  permanently  connected  together,  so  that  the  coherer  no  longer  is  operative  to 
signals,  and  must  be  replaced  by  a  new  one.  Then  again,  the  speed  at  which  the 
coherer  will  receive  messages,  is  not  above  fifteen  words  per  minute,  which  is  rather 
inconvenient,  considering  that  forty  words  per  minute  are  transmitted  with  the 
modern  systems  and  received  without  difficulty  with  other  detectors.  The  coherer 
having  such  a  multitude  of  disadvantages,  was  quickly  abandoned  for  the  detectors 
offering  better  characteristics.  The  coherer  possessed  one  great  advantage,  and 
that  was  the  fact  that  it  could  operate  a  relay  which  in  turn  could  be  made  to  close 
electrical  circuits,  operate  a  Morse  recorder,  ring  a  bell,  or  do  other  duties  which 
the  modern  detectors  do  not  accomplish. 

Another  type  of  coherer  which  does  not  employ  the  filings,  is  the  Branly-Popoflf 
detector,  which  consists  of  three  oxidized-steel  pointed  rods  in  the  form  of  a  tripod, 
resting  on  a  steel  plate.  The  connections  are  similar  to  those  of  the  coherer,  the 
detector  being  connected  in  series  to  a  relay  through  a  dry  cell.  The  signals  cause 
the  small  steel  rods  to  cohere  more  firmly  to  the  steel  plate,  in  such  a  manner  that 
the  resistance  of  the  oxide  is  broken  down  and  allows  the  current  from  the  battery 
to  flow  through  the  relay  magnets.  The  relay  operates  a  magnetic  device  which 
tilts  the  tripod  arrangement  of  the  small  rods,  and  restores  the  originally  high 
resistance. 


SLABY-ARCO  VACUUM  COHERER  Fig.   1 


A  relay  for  electrical  purposes  consists  usually  of  a  pair  of  electro-magnets 
arranged  with  an  armature  or  moving  contact  bar  in  front  of  their  pole  pieces,  this 
contact  bar  being  normally  held  away  from  the  magnet  poles  by  a  spiral  spring  and 
whenever  a  current  passes  through  the  electro-magnet  coils,  the  armature  bar  is 
attracted  and  its  contact  closes  an  electrical  circuit  by  coming  in  contact  with  the 

Copyright  1912  by  E.  I.  Co. 


74 


WIRELESS  COURSE— LESSON  NO.  10 


stationary  electrode.  As  soon  as  the  current  ceases  to  flow  through  the  magnet 
windings,  the  armature  bar  is  released  and  the  contact  broken. 

Still  another  form  of  coherer  exists  in  the  detector  of  the  former  Lodge-Muir- 
head  system,  which  consists  of  a  steel  rotating  wheel  dipping  near  but  not  quite 
touching  a  pool  of  mercury.  A  contact  is  made  between  the  pool  of  mercury  and 
the  steel  wheel  when  the  signals  are  received,  but  upon  the  interruption  of  the 
signals,  the  mercury  ceases  to  make  contact  with  the  steel  wheel.  This  is  known  as 
the  self-restoring,  or  automatic  coherer,  since  the  decohering  is  accomplished  without 
any  additional  apparatus.  The  mercury  coherer  is  connected  to  the  relay  as  in  the 
other  preceding  coherers,  and  operates  on  the  same  principle.  It  is  far  more  reliable 
than  the  Marconi  filings  coherer,  and  has  been  found  to  be  very  efficient,  though 
it  is  not  employed  at  the  present  time. 

Another  form  of  coherer  is  known  as  the  auto-coherer,  and  was  used  in  the 
simpler  "Electro"  wireless  receiving  sets.  The  auto-coherer  consists  of  a  small 
glass  tube  filled  with  carbon  grains.  On  both  sides  of  the  grains,  plugs  of  brass 
which  have  been  silver-plated  to  increase  the  conductivity  are  inserted.  In  some 
instances,  iron  or  carbon  plugs  are  used,  though  it  is  largely  a  matter  of  choice. 
Fig.  1  illustrates  the  auto-coherer,  and  it  might  be  interesting  to  add  that  this  was 
the  type  of  detector  employed  by  Marconi  when  he  received  the  first  signals  trans- 
mitted across  the  Atlantic  Ocean  at  St.  John  in  1903.  The  auto-coherer,  contrary 
to  the  types  of  coherers  described  thus  far,  does  not  operate  a  relay,  inasmuch  as 
the  drop  in  resistance  is  too  slight,  but  it  is  used  in  connection  with  one  dry  cell 
connected  to  a  low  resistance  telephone  receiver  of  but  75  ohms.  High  resistance 
telephones  are  of  little  value  in  connection  with  this  detector,  since  the  drop  in 
voltage  of  the  detector  is  sufficient  to  operate  a  low  resistance  receiver.  The  signals 
are  exceedingly  loud,  though  the  disadvantage  exists  that  the  detector  is  microphonic 
in  action,  and  all  sounds  in  the  room  or  on  the  operating  table  will  be  plainly  heard 
in  the  telephone  receiver.  Fig.  2  illustrates  the  connections  to  employ  for  the 
telephone  circuit  of  this  detector,  and  it  will  be  noted  that  a  resistance  has  been, 
added  in  order  to  allow  a  better  adjustment  of  the  voltage,  though  this  may  be 
dispensed  with  if  desired.  The  auto-coherer  is  but  little  used  except  by  amateurs 
who  have  just  begun  to  experiment  in  wireless  telegraphy. 


DAG 


Fig.  2 


Under  the  crystal  rectifier  type  we  find  the  many  different  detectors  employed 
in  present  day  systems.  The  term  "crystal  rectifier"  was  suggested  by  Dr.  George 
W.  Pierce  of  Harvard  University,  in  place  of  the  cognomen  formerly  employed  to 
signify  certain  detectors  possessing  the  electrolytic  valve  or  rectifying  action,  these 
having  been  known  at  one  time  as  "thermo  electric"  detectors  due  to  their  action  not 
being  fully  understood. 

The  crystal  rectifying  detector,  which  may  consist  of  a  proper  crystal  or  set 
of  crystals  of  mineral  formation,  when  placed  in  a  wireless  receptive  circuit  possesses 
the  phenomenon  of  passing  a  current  in  one  direction  many  times  better  than  in  the 
other.  Hence,  when  an  oscillating  or  alternating  current  such  as  that  which  surges 
on  an  aerial  circuit  passes  through  the  detector,  the  rectifying  action  is  set  up  and 
results  in  the  produced  pulsating  direct  current  acting  on  the  telephone 


WIRELESS  COURSE— LESSON  NO.  10 


75 


receivers.  These  pulsations  of  current  flowing  in  the  telephone  receivers  cause  the 
diaphragms  to  be  alternately  attracted  and  released  giving  rise  to  the  familiar  buzzing 
sound  by  which  the  signals  are  read.  It  will  thus  be  noticed  by  the  student  that  the 
alternating  current  of  the  high  frequency  waves  flowing  through  the  receiving  circuit, 
is  rectified  so  that  all  the  same  polarity  impulses  are  caused  to  flow  through  the 
telephones,  while  the  other  polarity  impulses  flow  through  to  the  ground.  In  this 
manner  the  telephone  receivers  operate  on  direct  current  of  a  pulsating  nature,  result- 
ing in  the  aforesaid  buzzing  sound.  The  property  of  these  crystals  to  allow  current 
to  flow  through  in  one  direction  often  is  as  marked  as  400  to  1,  i.  e.,  negative 
or  positive  impulses,  as  the  case  may  be,  will  flow  through  400  times  easier  in  one 
direction  than  in  the  other,  thus  allowing  the  telephone  receivers  to  operate  prac- 
tically on  direct  current. 

The  silicon  detector  is  the  most  popular  type  of  crystal  rectifier  used  to-day. 
It  employs  a  piece  of  the  artificial  product  known  as  fused  silicon,  which  is 
manufactured  in  the  electrical  furnaces  at  Niagara  Falls.  Silicon  is  a  black  or 
sometimes  grayish  material,  very  hard  and  brittle,  and  resembles  coal.  It  has  a 
bright  silver  lustre,  especially  after  being  broken  and  exposing  a  fresh  surface. 

Silicon  is  usually  placed  in  a  metal  cup  or  special  clamp.  If  used  in  the  former, 
a  solder  or  other  metal  alloy  melting  at  a  low  temperature  is  employed  to  hold  the 
crystal  in  place  and  to  make  contact  with  same.  Woods  Metal,  which  can  be  purchased 
at  any  chemical  supply  house,  is  the  most  popular  material,  since  it  melts  at  an 
exceedingly  low  temperature.  Another  material,  Hugonium,  which  has  been  employed 
with  great  success,  is  the  new  substance  introduced  by  the  Electro  Importing  Com- 
pany. This  substance  is  a  metal  alloy  which  is  very  plastic  until  compressed 
around  the  crystal,  and  after  a  few  hours  it  sets  firmly  holding  the  crystal  in  place. 
The  use  of  this  material  greatly  improves  the  sensitiveness  of  the  crystal,  since  the 
heating  which  would  be  applied  to  the  solder  if  same  were  used  to  hold  the  crystal, 
is  eliminated.  Solder  should  not  be  used  if  possible,  for  it  causes  the  crystal  to 
lose  its  sensitiveness  to  a  great  extent. 


SWITCH 


Fig.  3 


Fig.  4 


A  very  popular  mineral  detector  is  shown  in  the  illustration  of  fig.  3,  in  which 
the  material  is  held  in  the  metal  cup.  As  will  be  noted  from  the  following  descrip- 
tions, other  crystals  may  be  used,  and  such  a  detector  is  therefore  known  PS  a 
"universal"  detector.  The  cup  is  itself  held  on  a  metal  spring  so  that  a  light 
tension  can  be  produced  between  the  crystal  member  and  the  upper  pointed  conU.i. 
This  contact  is  also  arranged  on  two  springs  which  may  be  varied  by  the  hard 
rubber  handle  adjustment  screw,  allowing  the  tension  at  the  contact  point  to  be 
varied  at  will.  By  turning  the  cup,  a  new  contact  surface  on  the  crystal  can  be 
obtained._  For  the  utilizing  of  this  universal  detector  for  other  crystals  which  do 
not  require  pointed  contacts,  a  flat  metal  disc  which  can  be  screwed  on  the  pointed 
contact,  is  supplied.  Thus  the  detector  can  be  used  for  any  type  of  crystal  which 
requires  either  form  of  contact.  This  detector,  which  is  supplied  by  the  Electro 
Importing  Company,  uses  the  Hugonium  compound  for  holding  the  crystal,  as 
described  above. 

In  the  foregoing  example  the  student  has  been  introduced  to  the  most  popular 
type  of  mineral  _  detector,  but  there  are  more  expensive  professional  types  in  which 
the  relative  position  of  the  crystal  and  the  contact  point  may  be  very  accurately 
and  positively  adjusted.  The  contact  point  in  the  ordinary  detector  is  generally  of 
brass,  but  it  has  been  ascertained  recently,  after  much  research,  that  generally  the 


76 


WIRELESS  COURSE— LESSON  NO.  10 


best  results  are  obtainable  when  the  metallic  contact  resting  on  the  silicon  is  of 
gold.  For  this  purpose,  the  student  may  employ  a  gold  stick  pin,  which  will  be 
found  to  give  excellent  results.  Steel  needles  are  also  found  to  give  good  results,  and 
fine  copper  wire,  resting  gently  on  the  crystal,  is  also  very  effective. 

Telephone  receivers  used  with  silicon  should  be  of  high  resistance.  For  the 
best  results,  telephone  receivers  of  at  least  2,000  ohms  per  pair  should -be  used,  and 
slightly  higher  resistance  windings  ,are  in  some  instances  found  to  be  even  better. 

Silicon  detectors,  as  in  the  other  crystal  types,  are  subject  to  disadvantages,  the 
most  important  of  which  is  the  fact  that  if  a  nearby  station  is  sending  when  the 
detector  is  being  used,  the  sensitiveness  will  be  destroyed.  This  is  probably  caused 
by  the  fact  that  the  heat  of  the  oscillations  passing  through  the  contact  of  the 
detector  causes  an  oxidizing  effect,  which  interferes  with  the  proper  action.  All 
crystal  detectors  aside  from  the  pyron  detector,  which  will  be  shortly  described, 
and  the  carborundum  type,  are  subject  to  this  disadvantage  on  the  passing  of  heavy 
high  frequency  current  such  as  that  of  the  home  station  or  nearby  transmitters. 
If  the  detector  is  short-circuited,  as  shown  in  the  fig.  4,  or  better  still,  arranged 
with  a  pole-changing  switch  so  that  the  leads  may  be  completely  „ disconnected  and  the 
detector  itself  short-circuited,  as  illustrated  in  fig.  5,  the  sensitiveness  can  be  preserved 
while  transmitting.  No  battery  is  necessary  with  silicon  detectors,  but  is  sometimes 
used,  the  negative  oole  connecting  to  the  silicon. 


TO  RECEIVING   CIRCUIT. 


POLE  CHANGING    Fig  5 
SWITCH. 


The  Pyron  detector,  which  was  developed  by  G.  \V.  Pickxird  of  Amesbury,  Mass., 
and  patented  by  him,  is  somewhat  similar  to  the  silicon  type  in  form  excepting 
that  the  upper  tension  spring  carrying  the  pointed  contact  is  wide  and  massive,  its 
adjusting  screw  being  of  a  very  fine  thread.  The  pyron  crystal  is  iron  pyrites,  the 
former  name  being  the  trade  name  under  which  the  detector  is  known.  Its  upper 
face  is  highly  polished  and  the  detector,  while  combining  high  sensitiveness  with 
other  numerous  features,  has  the  very  important  merit  of  withstanding  heavy  nearby 
discharges  without  being  knocked  out  of  adjustment,  and  for  this  reason  is  much 
in  use  in  the  United  States  Navy,  on  battleships. 

Another  type  of  crystal  detector  which  has  been  developed  by  G.  W. 
Pickard  and  is  strongly  covered  with  patent  rights,  is  the  Perikon  detector.  This 
detector  consists  of  two  crystals,  copper  pyrites  and  zincite,  held  in  firm  contact 
against  each  other.  The  mounting  of  these  two  crystals  is  exceedingly  clever,  the 
copper  pyrite  crystal  being  mounted  in  a  cup  on  a  rod  which  is  so  arranged  that  it 
can  be  swung  in  all  directions  and  contact  with  any  portion  of  the  crystals 
can  be  obtained.  The  zincite  crystals  are  in  turn  mounted  in  a  large  cup;  usually 
a  number  of  these  being  used.  The  two  crystal  surfaces  are  brought  into  a  firm 
contact  by  means  of  a  spring  which  can  also  be  varied.  The  Perikon  detector 
is  probably  the  most 'sensitive  of  the  crystal  rectifying  types,  though  this  is  largely 
a  matter  of  opinion.  The  authors,  after  extensive  experiments,  have  found  that 
Galena,  if  used  according  to  the  method  advocated  by  them  and  explained  itn  a 
later  description,  is  probably  the  most  sensitive  of  the  crystal  detectors,  and  more 
so  than  the  Perikon.  The  Perikon  detector  is  illustrated  in  fig.  6,  and  is  largely 
used  in  the  Navy  and  Army  wireless  stations  as  well  as  in  the  better  commercial 
stations.  Its  ease  of  adjustment  makes  this  detector  one  of  the  most  popular,  and 
it  produces  a  sharp  cle-ar  sound  in  the  telephone  receivers.  The  nearby  stations 
also  effect  its  adjustment  as  in  the  instance  of  the  silicon  detector.  To  overcome 
the  effect  of  the  strong  oscillations,  the  Perikon  detector  has  latelv  been  placed  in 
a  small  pool  of  oil,  so  that  oxidization  of  the  eleme.nts,  either  by  the  natural  action 


WIRELESS  COURSE— LESSON  NO.  10  77 

of  the  atmosphere,  or  the  more  rapid  effect  of  strong  signals,  are  reduced  to  a 
minimum.  It  is  well  to  state  that  galena  and  silicon  are  also  used  in  the  same 
manner,  and  in  fact  the  covering  of  these  detectors  with  dust-proof  covers  has* 
also  been  suggested  lately.  Such  precautions  prevent  the  oxidizatioji  of  the  crystals 
to  -a  great  extent,  and  the  absence  of  the  dust  renders  the  sensitiveness  much 
greater.  No  battery  current  is  employed  with  Perikon  detectors  usually,  and  the 
wiring  diagram  is  illustrated  in  fig.  7,  the  same  wiring  scheme  being  used  for  all 
the  other  crystal  detectors.  Battery  curre«nt  is  sometimes  used,  the  voltage  being 
very  low  and  regulated  by  a  potentiometer.  The  polarity  of  this  current  must  be 
such  that  the  positive  line  is  connected  to  the  copper  pyrites.  ? 


Fig.  6 

Galena  is  a  mineral  crystal  of  lead,  and  is  obtained  from  mines  practically  all 
over  the  world.  The  crystals  resemble  a  bluish  or  grayish  colored  substance, 
which  when  broken  forms  into  straight  surfaces  or  cubes.  These  surfaces  have  a 
bright  mirror  finish.  Galena,  more  so  than  silicon  or  the  other  crystals,  has  the  great 
disadvantage  of  being  difficult  to  obtain  for  use  in  wireless  telegraphy,  inasmuch 
as  some  pieces  may  be  very  sensitive,  while  other  pieces  will  be  of  little  use.  In 
fact,  pieces  taken  from  the  same  large  piece,  will  be  entirely  different,  one  probably 
very  sensitive,  and  the  other  of  no  use  at  all.  However,  by  buying  either  selected 
crystals,  or  large  single  pieces  which  can  be  broken  into  a  number  of  smaller 
ones,  it  is  possible  to  obtain  several  good  specimens. 

The  authors  have  performed  numerous  experiments  and  researches  on  galena, 
and  have  stated  that  it  is  the  most  sensitive  of  the  crystal  detectors  if  correctly  used. 
Galena  cannot  be  employed  between  two  flat  discs,  for  the  'broad  surface  contact 
in  this  case  does  not  allow  the  rectifying  valve  effect  to  be  marked.  For  this 
reason,  fine  contact  of  little  surface  should  be  used. 

In  the  experiments  the  contact  materials  of  various  types  W'ere  tried.  German 
silver  has  been  found  to  have  remarkable  advantages,  and  was  used  with  success 
for  long  distance  receiving.  Steel  needles  do  not  give  such  good  results.  The  sensi- 
tiveness of  galena  was  found  to  be  entirely  destroyed  by  the  heating  of  the  solder 
in  which  it  was  placed,  and  for  this  reason  the  solder  was  entirely  abandoned. 
Clips  to  hold  the  crystal  have  been  advocated  and  the  method  of  using  is  illustrated 
in  fig.  8.  The  most  satisfactory  arrangement  was  found  to  be  a  fine  wire  of  about 
No.  30  B.  &  S.,  bare  copper,  resting  lightly  on  the  surface  of  the  galena  crystal. 
The  illustration  of  the  detector  enables  the  student  to  make  a  galena  detector  which 
will  give  excellent  results.  With  such  a  detector,  signals  were  received  from  a 
5  K.  W.  station  over  a  distance  of  2,500  miles  using  a  foreign  grade  of  galena  and  a 
p-air  of  standard  3,200  ohm  receivers. 

Another  point  of  much  importance  discovered  by  the  authors  in  connection  with 
their  researches  on  galena  has  been  to  impregnate  the  crystals  in  oil.  If  galena 
crystals  are  laid  on  dean  white  paper  and  allowed  to  remain  for  any  length  of 
time,  it  will  be  noticed  that  the  paper  is  oil  marked.  This  naturally  would  indicate 
that  a  certain  amount  of  oil  is  present  in  the  galena.  It  was  learned  that  if  the 
crystals  were  placed  in  ordinary  lubricating  oil  of  a  thin  grade  and  allowed  to  remain 
for  over  a  day  and  then  removed,  the  signals  were  found  to  be  considerably  louder 
and  longer  distances  could  be  covered.  Following  these  experiments,  many  others 
have  lately  advocated  the  impregnation  of  crystals  in  oil,  owing  to  the  increased 
efficiency.  The  Radion  detector,  used  by  the  Radio  Company,  works  on  the  prin- 
ciple of  galena,  using  a  fine  copper  wire.  In  the  April,  1911,  issue  of  "Modern 
Electrics,"  the  student  will  find  a  few  points  on  the  use  of  galena. 


78 


WIRELESS  COURSE— LESSON 


Molybdenite  is  another  mineral  which  consists  of  many  layers  compressed 
together.  These  layers  can  be  taken  apart  and  resemble  lead  foil.  Molybdenite  is 
usually  employed  between  flat  contact  surfaces.  It  can  also  be  used  with  a  point, 
but  owing  to  its  softness,  a  point  is  not  convenient.  The  great  characteristic  of 
Molybdenite  is  that  it  can  withstand  the  passage  of  powerful  electrical  oscillations 
without  being  materially  effected  in  adjustment.  It  is,  however,  little  used,  inasmuch 
as  the  sensitiveness  is  very  low. 


a 


D     V 


—  G 


Fig.  7 


One  of  the  most  popular  types  which  has  become  universally  used  in  commercial 
stations  through  the  fact  that  it  can  withstand  powerful  oscillating  currents,  is  the 
Carborundum  detector.  This  detector  is  employed  with  battery  current  regulated 
by  an  adjustable  resistance,  the  voltage  being  from  1  to  1.2  volts  as  found  by  G.  W. 
Pickard.  Carborundum  is  a  product  of  the  electrical  furnace,  created  at  a  tempera- 
ture of  7,000  degrees  F.  and  is  a  combination  of  salt,  sand,  sawdust,  and  coke.  It 
is  an  exceedingly  hard  crystal,  and  when  employed  in  a  detector,  the  student  will 
discover  that  the  results  will  be  better  if  the  lengthwise  section  of  the  crystals  is 
used.  The  blue  colored  crystals  will  be  fou»id  to  be  the  best,  though  green  colored 
crystals  are  claimed  to  be  superior  to  any.  The  poorest  quality  are  those 
varying  from  a  black  to  a  gray  color.  This  detector  may  be  used  in  the  same 
wiring  diagram  as  th.at  of  the  electrolytic  detector  shown  later. 

Aside  from  crystal  detectors,  the  next  class  is  found  under  the  thermo-electric 
detectors.  These  operate  on  the  well  known  principle  of  thermo-electric  couples 
in  which  heat  applied  or  developed  at  the  junction  of  certain  different  metals  estab- 
lishes an  electro-motive  force.  Incoming  oscillations  disturb  this  current  and  pro- 
duce variations  thereof  which  are  perceptible  in  the  telephone  receivers. 

The  magnetic  detector  has  been  extensively  adopted  by  the  Marconi  Wireless 
Company  and  depends  for  its  action  on  the  phenomenon  of  magnetic  hysteresis, 
a  common  type  being  that  employing  a  continuous  moving  iron  wire  band  which 
passes  by  the  poles  of  two  adjacent  permanent  magnets.  The  variation  in  the 
hysteresis  action  is  caused  by  the  incoming  oscillations  and  manifested  in  the  tele- 
phone receivers  which  may  be  about  80  ohms  each.  The  wiring  of  the  magnetic 
detector  is  shown  in  fig.  9. 


COURSE— LESSON  NO.  10 


79 


The  electrolytic  type  of  detector,  which  was  largely  used  before  the  simpler 
crystal  types  were  introduced,  is  illustrated  in  fig.  10,  in  which  the  working  parts 
may  be  clearly  seen.  The  detector  consists  of  a  small  carbon  cup  which  is  filled  with 
a  solution  of  five  parts  of  pure  water  to  one  part  of  nitric  acid.  Into  this  solu-i 
tion  dips  a  fine  platinum  wire,  which  can  be  more  or  less  immersed  into  the  solution 
by  means  of  the  adjusting  handle.  The  action  of  the  electrolytic  type  of  detector 
is  dependent  upon  the  formation  of  gas  at  the  platinum  wire  surface,  which  insulates 
the  wire  so  that  the  current  from  the  battery  cannot  flow  through  the  solution. 
On  the  reception  of  the  oscillations,  the  fine  film  of  gas  is  punctured  by  the  high 
frequency  current  for  an  instant,  and  the  gas  immediately  forms  again  to  return 
the  detector  to  its  normal  condition.  Thus  the  battery  current  is  allowed  to  flow 
periodically  when  the  resistance  of  the  detector  is  lessened  by  the  oscillations,  and 
this  lowering  of  the  resistance  is  heard  in  the  telephone  receivers  as  a  buzzing  sound. 
The  electrolytic  detector  should  be  used  with  battery  current,  and  the  positive  lead 
should  be  connected  to  the  platinum  wire  in  all  instances,  for  otherwise  no  results 
of  any  importance  can  be  obtained.  A  potentiometer  is  employed  to  regulate  the 
current. 


CLIP 


ne. 


Fig.   8  Fig.   9 

(Courtesy  "Modern  Electrics.") 

Another   type   of  electrolytic   detector  which   varies   mechanically  from   the   fore- 
going inasmuch  as  no  liquid  is  employed,  is  the  Peroxide  of  Lead  detector,  similar 


Fig.   10 


Fig.    11 


to  that  shown  in  fig.  11,  which  was  developed  by  Hoosier  &  Brown.  An  improved 
type  is  handled  by  the  Electro  Importing  Company,  as  shown  in  the  foregoing 
illustration,  where  a  special  compressed  pellet  of  lead  peroxide  is  placed  betweetn  a 
lower  electrode  of  lead  and  an  upper  electrode  platinized.  This  detector  operates 
on  a  similar  principle  of  electrolytic  action  as  in  the  foregoing  type,  and  is  con- 
nected in  the  same  style  of  circuit  as  the  liquid  electrolytic  detector,  the  wiring 
of  which  is  shown  in  fig.  12. 


80 


WIRELESS  COURSE— LESSON  NO.  10 


A  very  important  and  growing  class  of  detectors  are  those  commonly  called 
vacuum  or  Fleming  valve  detectors.  The  usual  form  of  the  vacuum  detector  follows 
that  used  by  Fleming,  and  one  commercial  form  of  it  is  illustrated  in  fig.  13.  This 
type  is  the  result  of  the  extensive  experiments  on  the  part  of  the  Electro  Importing 
Company  and  is  very  efficient.  The  Electro  audion  or  valve  detector  consists  of  a 
glass  vacuum  bulb  containimg  two  tantalum  filaments  connected  in  series  with  a  lead 
taken  off  at  the  connecting  point  of  b'oth  filaments.  One  filament  is  used  at  a  time 


\ 

7" 

TC 

:=- 

S~~\  T^ 

-=: 
—  =: 

( 

\y  n 

—  v>   ^j~ 

JO                      r-» 

j 

p     ' 

1 

EC 

MC. 


Fig.  12 


(Courtesy  "Modern   Electrics.") 


and  if  it  should  become  exhausted,  the  other  one  may  be  resorted  to.  The  wiring 
diagram  is  shown  in  fig.  14,  and  it  will  be  noted  that  the  telephone  receiver  is 
connected  in  series  with  a  battery  of  30  volts  or  more.  The  filaments  are  connected 
in  series  with  a  rheostat  and  a  battery  of  four  volts.  One  small  wire  is  used  in  the 
shape  of  a  zig-zag  winding  and  is  called  the  grid,  while  the  other  electrode  is  the 
nickel  or  platinum  foil.  When  the  filament  is  raised  to  incandescence  by  the  battery 
current  passing  through  it,  negative  electrons  are  sent  off  from  it  and  render  the 
space  between  the  filament  and  the  foil  electrode  conductive  for  an  electric  current, 
provided  the  E.  M.  F.  producing  this  current  is  directed  from  the  foil  to  the  hot 
filament.  When  the  oscillating  currents  from  the  aerial  traverse  the  detector  the 
action  is  to  allow  more  current  to  flow  through  it  in  one  direction  than  in  the  other. 


Fig.   13 


Fig.   14 


In  all  detectors  of  the  crystal  type,  the  best  resistance  of  telephone  receivers 
is  from  2.000  to  3,000  ohms,  either  for  one  single  receiver,  or  for  the  combined 
resistance  of  a  pair.  For  the  electrolytic  detector,  the  resistance  of  the  receivers 
should  be  the  same.  For  the  auto-coherer  detector,  the  resistance  need  not  be  higher 
than  75  ohms,  since  the  drop  in  resistance  of  this  detector  is  very  pronounced.  In 
the  magnetic  detector,  the  resistance  of  the  telephone  receiver  need  not  be  grciiter 
than  80  ohms  each.  The  vacuum  valve  detector  can  be  used  with  2,000  or  3,000  ohm 
receivers. 


WIRELESS  COURSE— LESSON  NO.  11 


81 


Lesson  Number  Eleven 


AERIALS. 
THE  WIRES  OF  THE  WIRELESS. 

section  is  devoted  to  aerials,  and  naturally  there  have  been  many  different 
types  of  them  evolved  in  the  development  of  the  wireless  art. 
The  word  "antenna,"  meaning  a  feeler,  or  to  reach  out  and  feel,  was  formerly 
applied  to  the  network  of  wires  suspended  in  the  air  to  catch  the  wireless  signals, 
but  became  improper  when  applied  to  a  sending  aerial,  as  the  wire  was  an  "antenna" 
only  so  long  as  it  was  "feeling,"  so  to  speak,  for  the  wireless  waves  in  the  ether. 
Hence  the  term  "aerial"  has  been  universally  adopted  to  represent  the  wires  erected 
to  intercept  the  waves. 

Although  some  very  good  work  has  been  accomplished  without  the  use  of  an 
aerial  wire  system,  over  short  distances  of  30  to  50  miles,  all  radio-telegraphic  and 
radio-telephonic  stations  of  any  size  to-day,  employ  a  more  or  less  elaborate  aerial. 
As  in  many  other  branches  of  science,  the  simplest  device  is  the  best  generally,  and 
this  is  the  case  with  the  aerial. 

Primarily,  the  most  important  factors  are  to  have  the  aerial  wires,  run  as 
straight  as  possible,  of  some  good  continuous  conductor,  such  as  copper,  phosphor 
bronze,  aluminum,  antenium,  etc.,  and  to  have  as  perfect  insulation  between  the  aerial 
and  the  ground  as  can  be  obtained.  For  any  serious  work,  all  joints  in  wires  must  be 
thoroughly  soldered,  especially  on  aluminum  wires,  "alumunite"  solder  being  very 
efficacious  for  this  purpose. 

For  standard  aerial  construction,  stranded  phosphor  bronze  cable  has  been 
adopted,  as  the  stranded  wires  present  a  greater  surface  for  a  given  weight  of  wire, 
than  one  solid  wire,  and  the  high  frequency  wireless  currents  travel  only  a  short 
depth  below  the  surface  of  the  conductors.  Iron  wire  alone  for  aerial  conductors 
should  be  avoided,  as  the  iron  will  cause  an  electro-magnetic  reaction  on  the  oscillating 
currents  in  the  wire,  tending  to  choke  them  and  diminishing  their  strength;  but  copper 
clad  iron  wire  has  been  tested  at  the  College  of  the  City  of  New  York,  and  found 
satisfactory  for  the  purpose,  due  to  the  skin  effect  cited  above. 


1  Fig.  1 

As  aforementioned,  many  elaborate  types  of  aerials  have  been  advocated  and 
employed  from  time  to  time,  but  one  of  the  best  and  simplest  to  construct  is  that 
known  as  the  flat  top,  or  T  aerial,  as  seen  in  illustration  fig.  1.  This  aerial  will  of  course 
have  different  dimensions,  according  to  the  work  to  which  it  is  to  be  adapted  to. 
For  ordinary  small  stations  up  to  J4  K.  W.  capacity,  the  two  poles  at  the  ends  may  be 
about  50  feet  high,  and  50  to  75  feet  apart.  Two  spars  or  "spreaders,"  3  to  4  feet 
long,  and  sufficiently  stout,  are  secured  at  each  pole  top  by  a  rope  and  pulley  to 

Copyright  1912  by  E.  I.  Co. 


WIRELESS  COURSE— LESSON  NO.  11 


Fig.  2 

permit  of  lowering  the  aerial  for  repairs,  etc.  Bamboo  is  excellent  for  spreaders, 
being  very  light  and  strong.  Insulators  should  be  placed  at  points  indicated  in 
sketch  fig.  2  and  between  spreaders  and  aerial  wires  also,  to  prevent  leakage  of  the 
aerial  currents  to  ground.  Some  typical  aerial  insulators  are  portrayed  at  fig.  3. 

Most  aerial  masts  are  of  wood,  and  hence  no  trouble  is  experienced  by  disapation 
of  currents  set  up  in  them,  as  is  the  case  when  iron  masts  are  employed.  To  reduce 
this  loss  to  a  minimum,  when  utilizing  iron  masts  or  poles,  they  are  generally  insulated 
at  the  base,  even  such  large  ones  as  the  420  foot  steel  tower  of  Fessenden's,  at  Brant 
Rock,  which  sets  upon  a  pillar  of  glass. 


Fig.  3 

All  guy  wires  on  any  type  of  mast,  either  wood  or  iron,  must  be  broken  up 
into  sections  not  exceeding  20  feet  preferably,  by  the  interposition  of  strain  insulators 
at  these  distances  apart.  This  is  to  prevent  any  undue  surges  or  disapations  of 
wireless  currents  being  set  up  in  them  unnecessarily,  and  thus  causing  a  loss  in  the 
aerial's  efficiency. 

As  stated  above,  the  majority  of  aerial  masts  are  wooden  staffs,  of  one  piece 
or  several  joined  together  as  in  regular  flag-staff  work.  Many  stations,  especially 
experimental  ones,  make  use  of  an  iron  pipe  aerial,  as  shown  at  Fig.  4,  which 


Fig.  4 


Fig.  5 


consists  of  several  lengths  of  decreasing  sizes  of  pipe  joined  end  to  end  by  means 
of  reducing  bushings,  and  the  whole  well  guyed  in  position. 

A  simple  way  of  raising  aerial  masts  of  any  considerable  height,  is  to  plant 
another  short  staff  about  1-3  the  length  of  the  mast,  quite  close  to  the  base  of  it, 
and  raise  by  means  of  a  tackle,  as  illustrated  in  fig.  5.  Guy  ropes  should  be  slung 
from  the  mast  about  2/3  the  way  up,  to  permit  of  guiding  it  while  it  rises. 

It  is  usual  to  make  the  aerial  of  more  than  two  spans  of  wire,  so  that  a  greater 
conducting  surface  will  be  presented.  For  stations  up  to  1  K.  W.  size,  an  aeriat 
should  have  at  least  6  wires  spaced  not  less  than  2  feet  apart  or  greater  than  3  feet. 


WIRELESS  COURSE— LESSON  NO.  11 


83 


It  has  been  found  that  nothing  is  gained  by  placing  the  separate  spans  closer 
together  than  2  feet,  and  for  fairly  large  aerials,  3  feet  is  very  good  spacing. 

In  general,  other  things  being  equal,  the  greater  the  height  of  the  aerial  the 
greater  its  range,  either  transmitting  or  receiving,  but  the  range  is  also  largely 
influenced  by  the  number  of  strands  in  the  aerials,  and  where  the  height  is  limited, 
the  aerial  may  be  extended  so  that  it  covers  a  considerable  area. 

It  must  be  kept  in  mind,  that  as  more  wires  are  connected  on  parallel  to  the 
aerial,  to  give  it  greater  activity,  the  capacity  inherent  in  it  is  also  directly  increased, 
and  the  aerial  must  not  be  made  too  large  for  the  transmitting  transformer  to 
charge,  or  there  will  be  a  decrease  in  the  range  instead  of  an  increase. 

It  is  often  desirable  to  have  a  large  aerial  for  receiving  and  a  smaller  one  of 
the  proper  capacity  for  transmitting,  and  this  is  easily  and  readily  accomplished  by 
switching  in  say  half,  of  the  total  aerial  system  for  transmitting  and  all  of  it  for 
receiving. 


M.E. 


SVV/IREAERIAL  3  DirreflCNT  WAYS  or 

CLOseoArTo*  CONNECTING  4-Wif?r 

AERIA\-S 

Fig.  6 

(Courtesy  "Modern   Electrics.") 

Several  varieties  of  aerials  are  depicted  by  the  diagram  fig.  6,  type  5  being  the 
most  commonly  utilized.  Types  3  and  4  are  not  of  very  good  electrical  design,  and 
seldom  used  any  more.  Types  1,  2,  3,  5,  6  and  7  are  known  as  straightaway  aerials 
for  the  reason  that  all  the  wires  lead  straight  away  from  the  leading-in  wire  or 
"rat-tail."  Type5  4  is  a  looped  aerial,  and  this  scheme  of  bringing  down  two  leads 
from  the  same  aerial  has  been  widely  used. 


Fig.  7 


The  great  advantage  of  looped  aerials,  which  by  the  way,  are  generally  hooked 
up  straight  away  for  transmitting,  is  that  interference  and  static  currents  can  be 
eliminated  from  the  receiving  instruments  quite  successfully.  A  common  commer- 
cial type  of  looped  aerial  is  shown  at  fig.  7,  part  of  the  aerial  being  used  as  a  static 
loop,  and  the  other  part  as  the  receiving  loop.  The  static  loop  is  usually  grounded 
through  an  adjustable  inductance  (as  a  tuning  coil),  in  series  with  a  variable  con- 
denser. 


84 


WIRELESS  COURSE— LESSON  NO.  II 


A  diagram  of  the  immense  aerial  suspended  from  the  Eiffel  Tower,  1,000  feet 
high,  at  Paris,  is  portrayed  by  sketch  8.  The  separate  strands  are  left  open  at  top  and 
bottom;  the  lead-in  being  taken  off  as  shown,  somewhere  about  the  centre. 

The  length  of  the  aerial,  has  a  direct  relation  with  respect  to  wave-length  emitted 
from  it,  and  for  untuned  simple  transmitters,  such  as  a  spark  coil,  with  no  helix  or 
condenser,  the  approximate  wave-length  in  meters  is  the  length  of  the  aerial  win- 
from  the  spark  g-ap  to  end  of  aerial,  multiplied  by  four,  as  a  factor.  For  tuned 
systems,  the  relation  for  wave-length  is  different  and  more  complex,  taking  into 
account  the  inductance  and  capacity  in  the  closed  oscillating  circuit,  shunting  the 
spark  gap,  and  will  be  treated  on  in  a  later  book. 


OLD  PLANT 


M.C- 


Fig.  8 


(Courtesy  "Modern   Electrics.") 


For  common  tuning  coils,  consisting  of  a  layer  of  insulated  wire,  wound  on  a 
circular  tube,  with  a  moving  contact  passing  over  its  various  turns,  the  relation 
may  be  assumed,  that  only  one-quarter  the  actual  wave-length  desired,  is  necessary 
on  the  coil  or  the  length  of  wire  on  the  coil,  in  meters*,  times  four,  equals  the  wave- 
length capacity  of  the  coil.  This  does  not  hold,  however,  for  loose-coupled  tuning  coils. 

The  so-called  umbrella  form  of  aerial  has  been  experimented  with  considerably, 
the  aerial  taking  its  name  from  the  fact  that  it  resembles  the  ribs  of  an  umbrella  in 
form. 

During  some  recent  elaborate  tests  carried  out  by  the  U.  S.  Naval  Wireless 
Laboratory,  under  the  direction  of  Dr.  L.  W.  Austin,  between  the  Brant  Rock,  Mass.. 
station  of  Fessenden,  and  the  scout  cruisers  Salem  and  Birmingham,  it  was  found 
thrt  the  umbrella  aerial  at  Brant  Rock,  420  feet  high,  was  equivalent  only  to  a  flat 
top  type  170  feet  high,  for  sending  purposes,  while  for  receiving  purposes  the  reverse 
was  the  case,  the  umbrella  type  proving  much  superior  to  the  flat  top.  Hence  an 
umbrella  aerial  is  a  better  receiver  than  a  radiator. 

It  might  be  well  to  give  a  few  dimensions  on  the  Brant  Rock  aerial,  as  it  is  one 
of  the  largest  in  use,  being  employed  for  wave-lengths  up  to  4,000  meters. 

The  support  for  the  aerial  wires  is  composed  of  a  steel  tower,  420  feet  high 
and  3  feet  in  diameter,  resting  on  a  well  insulated  base,  to  prevent  ground  leakage. 
Four  arms,  50  feet  in  length,  extend  from  the  top  of  the  tower,  and  from  each  of 
these,  two  300  cylindrical  cages  are  drawn  out  by  means  of  guys  at  an  angle  of  about 
45  degrees.  This  forms  a  system  of  eight  conductors  placed  symmetrically  about 
the  tower  to  form  an  umbrella. 

The  cages  are  about  4  feet  in  diameter,  consisting  of  four  wires  each,  kept  apart 
by  a  series  of  hoops  or  separators.  The  cages  are  insulated  from  one  another  at 
the  bottom  and  electrically  connected  to  the  steel  tower  at  its  top. 

The  inductance  of  the  complete  aerial  system  is  .055  millihenry,  and  the  inherent 
capacity  .0073  microfarads. 

All  the  guy  wires  are  thoroughly  insulated  by  large  strain  insulators  interposed 
every  40  to  50  feet. 

A  typical  commercial  aerial  for  long  distance  work  is  illustrated  by  the  cut 
fit?.  9.  This  aerial  formerly  served  on  top  of  the  Waldorf-Astoria  Hotel,  New  York 
City,  and  had  a  span  between  towers  of  236  feet.  The  steel  towers  are  each  84  feet 
high,  and  the  height  of  the  aerial  above  the  ground  was  300  feet.  This  aerial  was 
used  in  conjunction  with  a  5  K.  W.  transmitting  set. 

One  very  important  point  about  aerials,  is  that  they  tend  to  gather  static 
charges  from  the  atmosphere,  especially  during  thunder  storm  weather.  The  best 
expedient  to  follow  under  these  conditions  is  to  ground  the  aerial  to  a  good  earth 
(a  water  pipe  is  best),  by  connecting  through  a  knife  switch  and  a  length  of  No.  4 
B.  &  S.  copper  wire,  run  on  porcelain  knobs,  in  as  straight  a  line  as  possible,  avoid- 
ing any  sharp  bends  or  curvatures.  Lightning  and  static  currents  are  highly  oscil- 
latory in  nature  and  do  not  like  sharp  bends  in  their  path,  preferring  to  leap  to  some 
other  nearby  conductor  before  following  such  paths.  Lightning  switches  are  best 

*1  meter  equals  39.37  Inches. 


WIRELESS  COURSE— LESSON  NO.  11 


85 


Fig.  9 


(Courtesy   "Modern   Electrics.") 


placed  outside  the  building,  and  should  have  a  capacity  of  100  amperes,  with  fireproof 
base. 

Having  a  well  set-up  aerial,  thoroughly  insulated  and  correctly  designed,  its 
operating  efficiency  depends  in  great  part  upon  the  method  of  bringing  in  the  lead 
wires  to  the  instrument  room.  There  are  a  number  of  commercial  lead-in  insu- 
lators on  the  market,  one  of  which  is  shown  at  fig.  10,  this  particular  one  being 
composed  of  two  fibre  tubes,  one  sliding  within  the  other,  adapting  it  to  walls  of 
varying  thicknesses. 


Fig.   10 

A  lead-in  insulator  for  high  voltages  should  have  its  length  divided  up  into 
several  corrugated  or  projecting  ribs,  so  as  to  give  a  longer  path  along  it,  for  leakage 
of  the  currents.  Some  of  this  type  are  made  of  electrose  composition. 

At  fig.  11  is  a  view  of  a  typical  umbrella  aerial,  of  simple  construction,  this 
particular  one  being  famous  as  the  first  one  transmitting  a  wireless  message  (not 
dots),  90  miles  over  land  and  water,  when  charged  by  a  1-inch  spark  coil*,  excited 
from  a  6  volt  storage  battery,  using  the  regular  coil  vibrator.  This  record  is  official, 


Fig.   11 
*Electro  Importing  Company,  stock 'coll. 


(Courtesy  "Modern  Electrics.") 


86 


WIRELESS  COURSE— LESSON  NO.  11 


and  is  all  the  more  remarkable,  in  that  no  helix  or  condenser  were  employed,  the  self- 
inductance  and  capacity  of  the  aerial  and  ground  being  sufficient. 

The  aerial  shown,  comprises  4  separate,  4  wire  aerials  spaced  90  degrees  apart. 
The  wire  was  No.  14  B.  &  S.  copper,  with  each  strand  spaced  4  feet  from  the  next 
one.  The  aerial  was  stretched  from  a  tank  on  top  of  a  seven-story  building,  and  the 
total  amount  of  wire  in  the  aerial  was  7,000  feet. 


Fig.  12 

The  secret  of  charging  this  immense  spread  of  wire  lies  in  the  fact,  that  all  four 
aerials  were  connected  on  multiple  to  the  coil  spark  gap.  Each  4  wire  aerial  com- 
prised a  loop  aerial,  in  the  way  the  lead-in  wires  were  attached,  and  for  receiving, 
any  combination  of  looped  aerial  could  be  utilized. 

There  have  been  numerous  attempts  made  to  concentrate  the  direction  of  the 
wireless  waves  emitted  from  the  aerial,  and  there  is  quite  some  difference  apparent 
in  the  case  of  oblique  or  inclined  aerials.  When  an  aerial  is  slanting,  in  the 
direction  shown  at  fig.  12,  the  direction  of  the  greatest  activity,  is  that  taken  by 


. 

B-SMALL'T'SHOWT  OI«T»N«  Afn-H. 
C«c'-**TS  Ore  3t>i-rcjan>oirOiiHcr>Yf/ 
D-  AtttlAL.  Svonen.  •»B«». 


Fig.   13 


(Courtesy  "Modern   Electrics.") 


the  arrow.  On  this  assumption,  there  are  in  use  a  few  directive  aerials  which  give 
good  satisfaction,  and  a  readily  adjustable  form  of  directive  aerial  is  depicted  by 
diagram  13,  which  has  a  lead  from  each  separate  leg  of  the  umbrella  aerial,  brought 
to  a  switch  point,  so  that  any  one  or  more  of  them  can  be  quickly  thrown  into 
circuit. 

Probably  the  most  efficient   method  devised  so  far  to  direct  the  waves   toward^  a 
certain  point  by  means  of  the  aerial,  is  that  evolved  by  two  Italian  scientists,  Bellini 


WIRELESS  COURSE— LESSON  NO.  11 


87 


and  Tosi.  Diagram  14  will  serve  to  explain  the  action  of  their  system.  In  con- 
nection with  their  particular  aerial  arrangement,  they  used  a  "radio-goniometer,"  a 
view  of  which  appears  at  fig.  15.  The  radio-goniometer  consists  of  three  separate 
coils  of  wire,  one  being  movable  within  the  other  two.  The  aerial  takes  on  a  triangular 
form,  as  shown  in  diagram  at  E  and  F,  where  G  is  the  mast.  Two  sets  of  triangular 
aerials  are  utilized,  each  aerial  being  connected  to  one  of  the  radio-goniometer  coils, 
while  the  usual  sending  apparatus  is  connected  to  the  inner  moving  coil  S. 

The  action  of  the  individual  mast  systems  (Al,  Bl  and  AB)  is  as  follows: — 
When  waves  are  set  up  in  the  system  AB,  the  waves  are  given  off  in  a  general  front 
and  back  direction  from  the  plane  AB,  and  not  from  the  sides,  seeing  that  at  the  sides 
the  effects  of  the  two  nearly  vertical  wires  are  neutralized. 

In  the  same  way  the  second  system,  Al,  Bl,  emits  waves  at  right  angles  to  the 
former  set.-  If  now,  the  two  systems  are  excited  simultaneously,  the  resultant  effect 
will  be,  that  waves  are  emitted  in  a  certain  direction  only,  depending  upon  the 
relative  value  of  each  circuit.  Thus  if  A  B  is  excited  separately,  the  waves  will 
naturally  be  in  the  horizontal  direction,  and  Al  and  Bl  would  emit  waves  in  the  vertical 
sense;  with  both  systems  excited  equally,  the  waves  will  proceed  at  an  angle  of 
45  degrees,  and  so  on. 

To  excite  the  aerial  circuits,  use  is  made  of  the  middle  coil  S,  on  the  radio- 
goniometer. When  the  coil  S  is  placed  parallel  to  the  coil  M,  it  has  an  inductive 
effect  upon  this  coil,  and  no  effect  upon  the  second  coil;  therefore  the  aerial  system 
A  B,  is  excited  separately  and  the  waves  are  horizontal  or  east-west.  Placed  parallel 
to  coil  N,  the  result  is  that  the  waves  are  vertical  or  north-south.  When  at  45 
degrees,  it  has  an  equal  effect  upon  the  two  coils  and  the  waves  are  now  at  45  degrees, 
or  northeast-southwest.  Turning  through  any  other  angle,  the  wave  direction  follows 
this  angle  and  all  around  the  horizon. 


M,E. 


Fig.   14 


(Courtesy  "Modern  Electrics.") 


Fig.   15 


However,  the  waves  still  follow  two  directions,  (north-south),  and  it  is  desired 
to  cut  off  the  waves  in  one  direction,  so  that  we  only  have  the  north-directed  waves, 
for  instance.  When  this  is  accomplished,  a  truly  directive  aerial  system  is  the  result. 
Bellini  and  Tosi  have  done  this  by  using  a  simple  vertical  aerial  at  G,  in  the  centre 
of  the  crossing  triangular  aerials.  This  straight  aerial  wire  acts  to  cut  off  all  the 
waves  proceeding  toward  the  rear,  and  only  allows  the  front  waves,  so  to  speak, 
to  be  sent  out  into  the  ether,  thus  making  it  possible  to  direct  the  messages  to  a 
predetermined  point  anywhere  on  the  horizon. 

In  practice,  the  single  aeri-al  is  first  employed,  and  when  a  message  comes  in. 
the  combined  system  is  placed  into  circuit,  and  the  radio-goniometer  turned  until  the 
position  where  the  signals  come  in  loudest  and  clearest  is  reached.  A  duplicate 
instrument  is  used  for  sending  messages,  and  when  its  indicator  is  on  the  same 
point  as  the  receiving  radio-goniometer,  messages  can  be  transmitted  to  that  particu- 
lar station  alone. 

With  the  Bellini-Tosi  directive  aerial,  the  position  of  a  distant  station  can  be 
found  to  within  one  degree. 

At  fig.  16,  is  given  a  sketch  for  a  good  serviceable  aerial  of  the  straightaway 
type,  suitable  for  all  around  work,  both  transmitting  and  receiving. 


86 


WIRELESS  COURSE— LESSON  NO.  11 


10O  TO  2SO  FT — 

/ — SOLDERED  JO/NTS 


£LECTROSE 


® 


Fig.  16 


The  aerial  may  be  as  large  as  possible,  but  not  larger  than  200  to  250  feet  pre- 
ferably, except  for  heavy  commercial  work,  where  long  wave-lengths  are  most 
always  used.  Amateur  stations  cannot  use  over  200  meters  wave-length. 

The  aerial  wire  may  be  No.  12  B.  &  S.  solid  copper,  antenium,  or  stranded 
phosphor  bronze  wire,  and  these  are  easily  soldered.  Each  strand  should 
be  separated  from  the  spars  by  a  good  sized  insulator,  of  sufficient  strength  to 
hold  the  discharge  from  the  transmitting  set,  without  leakage.  Additional  insulators 
may  be  placed  in  the  spar  ropes  as  shown,  if  desired,  but  are  not  necessary,  if  the 
insulators  on  the  aerial  spans  are  of  sufficient  size. 

The  lead-ins  are  taken  off  at  the  centre  of  the  spans,  soldering  the  joints  thor- 
oughly, and  joining  them  all  together  before  they  enter  the  wireless  room,  or  every 
three  leads  may  be  joined  together,  and  the  two  leads  thus  formed  brought  down, 
making  a  loop  aerial. 

The  spars  are  generally  of  hard  wood,  such  as  spruce,  oak,  etc.,  and  bamboo  or 
iron  pipe  may  be  substituted.  All  the  ropes  for  this  work  should  be  tarred  or  waxed,  to 
give  them  greater  serviceability  and  stability.  Fig.  17,  shows  a  simple  and  effective 
method  of  arranging  the  aerial  in  connection  with  a  counterbalance  weight,  W,  at 
the  end  of  the  rope  supporting  the  aerial.  This  automatically  takes  up  the  stretch- 
ing and  shortening  of  the  rope  due  to  climatic  conditions.  Some  aerials  are  erected 
with  spiral  springs  in  the  supporting  ropes,  which  also  compensate  for  ordinary 
changes  in  the  rope,  etc. 

POLE 


Fig.  17 

In  general,  the  height  of  the  aerial  determines  the  range  of  a  wireless  station, 
transmitting  and  receiving,  but  of  course  a  large  part  of  this  is  dependent  upon 
the  apparata  used. 


WIRELESS  COURSE— LESSON  NO.  12 


Lesson  Number  Twelve 


THE  HOOK-UPS  AND  CONNECTIONS. 

A  GREAT  part  of  the  success  in  wireless  telegraph  or  telephone  work,  devolves 
upon  the  correct  connection  of  the  various  instruments  to  each  other,  and  to 
the  aerial  and  ground. 

We  will   take  up  the  proper  connections   of  the  Transmitting   Circuits   first,   but 
before   starting,  a   foreword   on   the   reading  of   diagrams   may   be  helpful.     To   those 

STUDY  OF  THE  DIAGRAMS. 


AERIAL- 


GROUND.         COHERER.     DECOHEI=?ER, 


CARBON         SILICON          PERIHON 
DETECTOR.    DETECTOR.    DETECTOR. 


U 


ELECTROLYTIC, 
DETECTOR. 


AUDION 
DETECTOR.      RHEOSTAT.      RHEOSTAT: 

< 


VARIABLE 
giNSLE  RECEIVER  DOUBLE  RECEIVER    Co NDENSER    CONDENSER 

Wireless  Telegraph   Symbols. 

(Courtesy    "Modern    Electrics.") 


unfamiliar  with  wiring  diagrams  a  first  glance  is  more  or  less  confusing,  generally, 
due  to  the  fact  that  a  clear  working  idea  of  the  different  distinct  circuits,  is  not 
seen  in  the  mind.  To  read  diagrams  quickly,  necessitates  a  well  memorized  knowl- 
edge of  the  various  individual  circuits  and  when  several  circuits  appear  together 
in  one  sketch,  the  correct  way  of  reading  it,  is  to  search  out  each  individual  circuit 

Copyright  1912  by  E.  I.  Co. 


90 


WIRELESS  COURSE— LESSON  NO.  12 


STUDY  OF  THE  DIAGRAMS.— (Continued.) 

correctly  first,  and  then  the  next,  and  so  on.  To  illustrate;  let  the  diagram,  fig. 
1,  be  taken  for  an  example.  This  is  a  simple  hook-up  for  a  spark  coil,  battery,  key, 
spark  gap,  condenser,  aerial  and  ground. 

First,  it  is  known  that  the  spark  coil  has  two  windings  on  it,  a  primary  or  battery 
coil  P,  and  a  high  voltage  secondary  coil  S.  Hence,  it  is  a  simple  matter  to  trace 
out,  first,  the  primary  circuit,  from  primary  coil  P,  to  key  K,  battery  B,  and  thence 
back  to  primary  coil  P,  completing  the  circuit. 

Glancing  at  the  secondary  circuit,  it  is  best  to  notice  first  that  the  secondary 
coil  S  terminals,  are  connected  to  the  aerial  A,  and  ground  G,  and  then,  that  the 


TUNER.       DOUBLE  SLIDE  TUNER-  QSCIL 


HELIX- 


COIL  OR  TRANSFORMER.    CONDENSER. 


' 


e — o  o — ° 


I      O 

o  v"     \    o 


GAP.       3-R.D-T. SWITCH, 


POTENTIOMETER.    ADJUSTABLE  CONDENSER-CHOKE  COIL.. 

Wireless  Telegraph   Symbols. 

(Courtesy    "Modern    Electrics.") 


condenser  C,  is  shunted  across  the  spark  gap  S  G,  which  checks  off  the  whole 
diagram.  Of  course,  a  good  store  of  working  knowledge  regarding  the  exact 
action  and  inter-action  of  the  separate  apparata  is  absolutely  essential  before  attempt- 
ing to  read  any  fairly  complicated  diagrams.  A  list  of  symbols,  used  in  wireless 
diagrams  appear  on  the  first  and  second  page. 

In  fig.  1,  is  depicted  the  simplest  transmitting  hook-up  used  for  sending  wireless 
messages,  excepting  the  condenser,  which  has  been  added  here.  Most  all  wireless 
stations,  of  any  size  from  a  1  inch  spark  coil  up,  employ  a  helix  and  condenser 
in  the  secondary  circuit  to  permit  of  tuning  the  apparata  or,  in  other  words,  per- 


WIRELESS  COURSE— LESSON  NO.  12 


91 


mitting  of  varying  the  length  of  the  emitted  wave,  which  is  not  possible  with  the 
simple  hook-up  just  cited,  except  if  a  different  length  of  aerial  wire  was  used  for 
different  wave-lengths. 

The  commonest  tuned  transmitting  arrangement  is  shown  in  fig.  2.  where  H 
is  a  helix  of  several  turns  of  large  wire,  forming  a  tuning  coil  or  variable  inductance, 
allowing  more  or  less  of  the  turns  to  be  put  in  series  with  the  aerial,  which  causes 
a  change  in  the  wave-length  sent  out.  The  system  here  given,  conforms  to  the  type 
known  as  "close-coupled,"  owing  to  the  fact  that  but  one  transformer  coil  or  helix 
is  utilized.  Sometimes  it  is  called  a  "tight"  coupling. 

The  circuit  around  the  helix  winding,  condenser  and  spark  gap,  constitutes  the 
closed  oscillating  circuit  through  which  the  high  frequency  surges,  set  up  by  the  rapid 
charging  and  discharging  of  the  condenser  pass.  This  excites  the  helix,  the  same 
as  a  transformer,  but  the  one  winding  has  to  serve  the  dual  purposes  of  primary 
and  secondary  coils  here;  the  helix  secondary  current  flowing  out  through  the  aerial 
and  to  the  ground,  charging  them  both. 


P        S 


Fig.    1  Fig.   2 

(Courtesy  "Modern  Electrics.") 

A  similar  transmitting  set  to  that  mentioned  in  fig.  2,  is  illustrated  by  fig.  3, 
only  a  transformer  operating  directly  on  alternating  current  here  takes  the  place  of 
the  spark  coil  and  battery.  The  transformer  is  indicated  by  T,  and  an  adjustable 
choke  coil  to  limit  the  value  of  the  current  used,  C  C;  K  being  the  key,  of  substan- 
tial construction  to  stand  the  heavy  current. 

At  fig.  *  is  given  a  layout,  for  the  connecting  up  of  an  electrolytic  Interrupter, 
I;  choke  coil,  C  C;  and  spark  coil,  with  same  secondary  connection  as  before.  This 
type  of  circuit  is  much  used  in  amateur  stations,  with  more  or  less  modifications. 

A  diagram  for  a  transmitter  employing  a  loose-coupled  tuning  coil  or  helix 
instead  of  the  single  coil  helix,  is  outlined  at  fig.  5.  The  primary  circuit  is  A  C. 
feeding  the  primary  of  the  transformer  T,  this  circuit  including  also  a  voltmeter,  and 
an  ammeter  for  noting  the  amount  of  current  and  voltage  passing  into  the  trans- 
former. 


® 


Fig.  3 


'  "Fig.  4 


iNPf  DMMCC  C*<~ 


(Courtesy  "Modern  Electrics.") 


fne'n*l«se4  oscillating  circuit  here  comprises  the  condenser,  spark  gap,  and  primary 
coil  P,  of  the  sending  loose-coupler,  or  transformer.  The  oscillating  high  frequency- 
currents  surging  through  the  loose-coupler  primary,  which  is  in  close  proximity  to 
the  secondary  coil  S.  sets  up  another  current.of  higher  voltage  and  similar  fre- 


92 


WIRELESS  COURSE— LESSON  NO.  12 


quency  in  it.  This  excites  the  aerial  and  ground,  the  aerial  current  passing  through 
a  hot-wire  ammeter  and  loading  coil  A  L,  the  meter  denoting  when  the  maximum 
current  is  being  radiated. 

A  complete  wiring  plan  appears  at  fig.  6,  for  a  fairly  complete  transmitting 
plant.  The  apparatus  included  here  is  as  follows:  Regular  wireless  transformer 
T.  small  key  K  and  condenser  C,  operating  a  magnetic  key  R,  choke  coil  R  C, 
Voltmeter  V  M,  Ammeter  A  M,  direct  reading  Wattmeter  W  M. 

The  secondary  circuit  comprises:  the  oscillation  transformer  O  T,  condenser  L, 
spark  gap  S  G  and  hot-wire  ammeter. 

The  wiring  diagram  for  a  sending  station  such  as  used  on  shipboard  for  com- 
mercial purposes  is  illustrated  by  fig.  7. 


Fig.   5 


Fig.  6 


This  set  makes  use  of  a  motor-generator,  the  motor  being  direct  current,  and 
the  generator  alternating  current.  The  motor  takes  its  current  from  the  D  C  mains 
through  a  starting  resistance  C  B,  and  field  rheostat  or  regulating  resistance  M  F  R. 
The  alternator,  driven  by  direct  shaft-coupling  with  the  motor,  delivers  a  suitable 
alternating  current  from  the  slip  rings  S  R  to  transformer  T,  with  the  voltmeter 
V  M,  ammeter  A  M,  wattmeter  W  M,  frequency  meter  F  M  and  adjustable  choke 
coil  C  C  interposed  in  its  primary  circuit.  Regulation  of  the  primary  transformer 
current  can  thus  be  governed  or  varied  by  adjusting  the  motor  field  resistance 
M  F  R;  the  alternator  field  rheostat  A  F  R;  or  the  choke  coil  C  C;  K  is  the  key, 
which  is  sometimes  a  magnetic  one. 


VM.  WM.  AM.    PM. 


M.S. 


D.C.  MAINS 


ALTERNATOR 
S 

'FIELDS  1       1 


® 


O.T. 


The  secondary  or  high  voltage  circuit,  is  the  same  as  previously  shown,  with 
the  exception  that  a  variometer  is  inserted  in  place  of  the  loading  coil,  which 
serves  the  same  purpose,  in  the  aerial  lead. 

The  Fessenden  High  Frequency  or  Singing  spark  system,  has  been  quite  exten- 


WIRELESS  COURSE— LESSON  NO.  12 


93 


sively  used  in  the  U.  S.  Navy,  and  a  diagram  of  the  general  layout  for  the  transmitting 
circuits  is  depicted  by  fig.  8. 

Referring  to  fig.  8,  the  D  C  mains  supply  a  motor  driving  the  500  cycle  alternator 
ALT,  and  on  the  same  shaft  with  these  two  machines,  is  mounted  the  synchronous 
rotary  spark  gap  S  Y  N  rotating  in  step  with  the  alternations  of  current,  causing 
the  sparks  to  occur  in  the  two  gaps  SGI  and  S  G  2  at  periods  of  maximum  activity 
in  each  alternation. 

A  common  key  K,  operates  the  transformer  through  the  medium  of  a  special 
magnetic  key  M  K;  C  1  and  C  2  are  compressed  air  condensers,  having  safety 
spark  gaps  S  F  1  and  S  F  2  connected  across  them  to  prevent  puncture  under 
severe  strains.  G  2  is  the  discharge  ground  ball  for  the  safety  gaps. 

The  helix  is  a  loose-coupled  affair,  in  three  sections,  allowing  any  combination 
of  coupling  to  be  readily  effected.  P  is  the  primary,  S  1  and  S  2  the  secondaries. 

The  secondary  circuit  leads  through  a  hot-wire  ammeter  M  to  the  aerial,  which 
is  of  net-like  construction,  there  being  a  number  of  cross  connecting  wires  attached 
to  the  regular  spans,  the  idea  being  to  imitate  a  solid  radiating  surface  as  near 
as  possible;  G'  is  the  ground  for  the  open  oscillating  circuit. 

The  connection  of  a  "Telefunken"  quenched  spark  gap  or  series  gap,  into  a 
common  transmitting  set  is  shown  at  fig.  9.  For  tuning,  a  variometer  is  depicted 
but  a  helix  may  be  utilized.  To  realize  the  high  efficiency  of  the  Telefunken 


Fig.  8 


system,  500  cycle  primary  current  must  be  used  for  the  transformer,  which  gives 
the  singing  note  so  penetrating  in  cases  of  bad  static  or  interference. 

Attention  will  now  be  turned  to  the  receiving  apparata  and  the  best  methods 
of  connecting  it  for  efficient  results. 

The  very  simplest  receiving  diagram,  is  that  shown  at  fig.  10,  the  functions 
involved  being  the  antenna,  a  microphone  or  carbon  detector  D,  battery  B,  telephone 
receiver  R,  and  ground  connection  G,  the  latter  of  which,  for  short  distances  may  be 
unemployed. 

Practically  all  wireless  stations  at  the  present  time  employ  a  type  of  detector 
which  necessitates  the  use  of  telephone  receivers  to  read  the  signals,  but  the  first 
Marconi  apparatus  used  a  coherer  or  filings  tube  detector,  and  a  wiring  scheme  for 
a  good  working  coherer  set,  is  illustrated  in  diagram  fig.  11,  where  C  is  the  coherer; 
D  the  tapper  or  de-coherer;  T  tuning  coil;  V  C  variable  condenser;  F  C  fixed  con- 


94 


WIRELESS  COURSE— LESSON  NO.  12 


denser;  R  high  resistance  relay  (preferably  polarized);  rheostat  R  2;  battery  B,  and 
choke  coils  A.  C. 

A  hook-up  for  a  simple  tuned  receiving  set  comprising  single  slide  tuning  coil 
T,  microphone  detector  D,  telephone  receivers  R,  battery,  aerial  and  ground,  is 
represented  at  fig.  12. 


A.C.MAINS 
6O-50O  CYCLES 


"OuOO? 


Fig.  9 


The  principal  detector  used  now  is  the  crystal  Silicon  or  Perikon,  a  diagram 
for  which  appears  in  fig.  13,  while  figs.  14-17  depict  other  connections  for  "close- 
coupled"  receiving  circuits  with  potentiometer  for  varying  the  amount  of  current 
supplied  to  the  detectors. 

Fig.  18,  shows  the  proper  connections  for  an  electrolytic  detector  and  a  testing 
buzzer  for  ascertaining  the  sensibility  and  adjustment  of  the  detector.  C  is  a  separate 
lixed  condenser. 


B 


(Courtesy  "Modern  Electrics.") 


Fig.   11 


While  "close-coupled"  tuning  coils  or  auto-transformers  have  been  largely  used, 
the  "loose-coupled"  or  two-coil  transformer  has  been  widely  adopted  because  of 
its  wider  range  of  selectivity,  and  other  possibilities. 

A  circuit  for  a  loose-coupler  L.  C.;  Silicon  detector  D;  fixed  condenser  F  C; 
telephone  receiver  R;  and  variable  condenser  V  C  is  given  in  fig.  19. 


WIRELESS  COURSE— LESSON  NO.  12 


95 


I 


Fig.   12  Fig.   13 

(Courtesy  "Modern  Electrics.") 

It  may  be  noted  here  that  the  variable  condenser  is  inserted  in  the  ground 
connection,  and  whether  it  is  put  here  or  on  parallel  with  the  tuning  coil,  makes  a 
great  deal  of  difference,  in  the  receipt  of  certain  wave-lengths.  For  receiving  wave- 


T.C.    E- ELECTROLYTIC   DOTCTO* 
»« 


Fig.   14  Fig.  15 

(Courtesy  "Modern  Electrics.") 

lengths  shorter  than  that  of  the  natural  period  of  the  receiving  aerial,  the  variable 
condenser  is  inserted  in  the  ground  lead,  but  to  get  long  wave-lengths  the  capacity 
must  be  shunted  across  the  tuning  inductance.  It  is  a  very  good  idea  to  have  the 


WA 


-PT  SWITCH 


G    •=•        E-EtgCTROLVTie 
*  S~  Siuicotsi 

C-   CARBORONOU 


Fig.    16  Fig.    17 

(Courtesy  "Modern  Electrics.") 

variable  capacity  connected  to  a  throw-over  switch,  as  in  fig.  20,  so  that  it  can  be 
quickly  changed  when  desired  from  one  connection  to-  the  other.  In  this  cut,  is 
also  shown  a  variometer  in  the  aerial  lead,  to  give  additional  wave-length  capacity 
to  the  receiving  set. 


> 


WIRELESS  COURSE— LESSON  NO.  12 


A  very  good  receiving  set  is  shown  by  the  arrangement  at  fig.  21,  where  the 
secondary  of  the  loose-coupler  is  divided  up  into  several  steps,  and  both  a  loading 
coil  and  variometer  are  used  in  series  with  the  aerial.  The  tuning  coil  T  C  and 


rS 

!!    r 

-s 

B 

sr 

Xj 

n 
O 

f5 

>)R~ 

Fig.   18  Fig.   19 

(Courtesy  "Modern  Electrics.") 

variable  condenser,  are  used  to  cut  out  static,  etc.  It  is  advisable  to  have  a 
circuiting  switch  around  the  variable  condenser  in  series  with  the  tuner,  to 
out  when  not  wanted,  such  as  when  receiving  long  wave-lengths. 


short- 
cut  it 


Fig.   20  Fig.   21 

(Courtesy  "Modern  Electrics.") 

In  sketch  22,  is  illustrated  diagrammatically,  the  Marconi  selective  receiving  set, 
or  "X"  stopper  as  it  is  called.    All  the  tuning  inductances  are  single  coil  transformers. 


—  a, 


Fig.  22  Fig.  23 

(Courtesy  "Modern  Electrics.") 

Marconi's  "Interference  Preventer"  is  diagrammed  at  fig.  23,  and  employs  three 
loose-couplers,  one  being  in  the  local  detector  circuit.  The  static  coil  and  condenser 
is  also  shown. 

(To  be  continued  Lesson  Thirteen) 


WIRELESS  COURSE— LESSON  NO.  13 


97 


Lesson  Number  Thirteen. 


THE  HOOK-UPS  AND  CONNECTIONS.— (Continued.) 
USEFUL  INFORMATION. 

A  receiving  set  much  used  by  the  U.  S.  Navy,  makes  use  of  a  loose-coupler 
with  adjustable  primary  and  secondary  inductances,  and  aerial  loading  coil.  The 
diagram  of  connections  for  this  set  are  at  fig.  24,  where  A  L  is  the  aerial  loading 


Fig.  24 


Fig.   25 


inductance,    L   C  loose-coupler,   V    C   a   .002    M.    F.    variable    condenser,    R    telephone 
receivers  of  high  resistance,  F  C  a  fixed  condenser,  P  T  potentiometer  and  auxiliary 


I 


Fig.  27 


resistance  P  R  of  1,800  ohms.     Perikon  detector  P  D  and  Pyron  detector  P  Y  con- 
nected   separately,    by    means    of    the    detector    switch    D    S.      A    testing    buzzer    is 


ME. 


(Courtesy  of  "Modern  Electrics.") 

indicated  by  B  Z,  with  push  button  T  K  and  battery  B  2.     The  detector  b'attery  is  at 
B    1.     One  of  the  most  efficient   receiving  devices  for   the   elimination    of  static   and 

Copyright  1912  by  E.  I.  Co. 


98 


WIRELESS  COURSE— LESSON  NO.  13 


severe  interferences  from  various  sources  is  the  Fessenden  "interference  preventer," 
which  is  shown  by  the  diagram  fig.  25. 

The  Fessenden  Interference  Preventer,  involves  the  use  of  two  loose-couplers, 
arranged  to  move  together,  as  regards  the  adjustments,  with  one  variable  condenser 
calibrated  to  read  .05  higher  on  each  scale  division  than  on  the  other  variable  con- 
denser. The  variometer  is  used  to  tune  with  in  connection  with  the  loose-coupler. 

The  switch  A,  is  closed  to  cut  out  static  currents,  and  the  variometer  adjusted 
until  it  disappears. 


Fig.   30  Fig.   31 

(Courtesy  of  "Modern  Electrics.") 

A  diagram  of  the  "Telefunken"  receiving  set,  with  variometer,  variable  condenser, 
galena-graphite  detector,  fixed  condenser,  and  head  telephones  is  shown  in  cut  26. 

The  "lopped"  aerial  or  divided  aerial  is  a  decided  advantage  for  sharp  clear 
tuning  of  wireless  signals,  a  common  method  of  utilizing  it  being  shown  at  fig.  27, 
in  connection  with  a  double  slide  tuning  coil. 


Fig.   32  Fig.  33 

(Courtesy  of  "Modern  Electrics.") 

A  looped  aerial  scheme  much  in  use  by  commercial  stations  is  that  in  fig.  28. 
The  400  meter  coil  and  variable  condenser  V  C  constitute  the  static  loop,  as  it  is 
called,  and  are  used  to  weed  out  static  or  "X." 

A  diagram  for  a  receiving  set,  including  looped  aerial,  four  variable  condensers, 
variometer,  and  loose-coupler,  is  shown  by  fig.  29. 


BlTIAK    KEY 


Fig.   34  Fig.   35 

(Courtesy  of  "Modern  Electrics.")  » 

A  duplex  receiving  set,  enabling  the  operator  to  receive  two  distinct  messages 
from  the  same  aerial  is  illustrated  by  cut  fie.  30.  It  is  best  used  with  two  separate 
pairs  of  receivers,  so  that  two  persons  may  listen  in  at  the  same  time. 

A  few   diagrams   will   now   be   given   attention   for   the   complete   wireless   station, 


WIRELESS  COURSE— LESSON  NO.  13  99 

i.  e.,  including  transmitting  and  receiving  instruments  with  throw-over  switches. 
Fig.  31,  shows  the  simplest  complete  transmitting  and  receiving  set  with  a  double- 
pole,  double-throw,  knife  switch  for  changing  from  one  to  the  other. 

Fig.  32,  portrays  the  station  circuits  for  tuned  sending  and  receiving  apparata 
with  lightning  grounding  switch,  and  testing  buzzer.  The  transmitting  instruments 
are  close-coupled  and  the  receiving  loose-coupled  in  this  instance. 

The  use  of  a  three-pole  aerial  switch,  on  the  pattern  of  the  De  Forest  type,  in 
combination  with  a  set  of  tuned  apparata  is  depicted  by  diagram  fig.  33. 


M 


(Courtesy  "Modern  Electrics.") 


Fig.  36 


The  practice  of  late,  has  become  common  to  eliminate  the  cumbersome  aerial 
switch  for  changing  over  from  sending  to  receiving,  by  the  substitution  of  an  automatic 
"break-key"  scheme,  or  a  system  whereby  the  transmitting  key  connects  the  receiv- 
ing instruments  after  the  sending  is  finished. 

One  method  of  accomplishing  this  idea  is  exemplified  by  the  drawing,  fig.  34, 
and  still  another  way  by  fig.  35. 


100,000 -v 
A.C 


BLOW  OUT  MAGNET 
CHOKE  COIL 
\     IIC \CJ 


5000- Y  DC 
GEN 


Fig.  37 

In  wireless  telephony  or  radiophony,  an  arc  of  some  form  is  generally  utilized 
to  generate  the  high  frequency  undamped  oscillation  or  waves,  the  original  Poulsen 
system  being  shown  in  fig.  36,  while  at  fig.  37,  is  exhibited  the  working  connections 
of  the  radiophone  system  developed  by  A.  Frederick  Collins. 

_n  the  Collins  system,  the  arc  takes  place  between  a  pair  of  rotating  electrodes 

i  with   blowout   magnets  as   shown.     The   arc   current   is   5,00\  volts   D.    C.     The 

variation   in   the  frequency  of  the  arc  current   is  accomplished  by  the   transmitter  T, 

transformer  coil,  and  25  volts  D.  C;  R  T  is  a  resonance  tube,  to  ascertain  when  the 

instruments  are  properly  tuned.     T  I  is  a  tuning  inductance. 


100 


WIRELESS  COURSE— LESSON  NO.  13 


On  the  receiving  side,  use  is  made  of  a  tuning  coil  T  C,  Condensers  C,  battery 
B,  Rheostat  R,  telephone  receiver  R,  and  a  special  thermo-electric  detector  D. 

The  "Audion"  detector,  developed  by  Dr.  Lee  De  Forest,  the  radiophonist,  is 
a  very  good  detector  for  radiotelegraphic  or  radiophonic  work,  and  is  connected  up 
in  the  manner  outlined  in  fig.  38. 


TANTAUUM 


-==•  GROUND 

M.E. 

(Courtesy  "Modern   Electrics.") 


Fig.   38 


USEFUL  INFORMATION. 


DIELECTRIC     STRENGTHS    OF 

VARIOUS  INSULATORS. 

Kilovolts    per    centimetre     required    to 

break  down  the  Insulator. 

MATERIAL. 

Micanite    4000 

Mica    2000 

American  Linen  Paper,  Paraffined..   540 

Ebonite    538 

Indiarubber    492 

Linseed  Oil   '. 83 

Cotton   Seed   Oil    67 

Lubricating   Oil    48 

Air   Film,  2  mm.  thick    57 

Air  Film,  106  mm.  thick 27 


NOTES  ON  ROPES. 

Hemp  Rope. — To  calculate  the  work- 
ing strain  of  rope,  square  the  circum- 
ference in  inches,  and  divide  by  8  for 
the  allowable  strain  in  tons. 

To  find  the  least  size  of  rope  to  lift 
a  given  weight,  multiply  the  weight  in 
tons  by  8  and  extract  the  square  root. 
The  number  found  is  the  circumference 
in  inches. 

Wire  Rope. — To  find  the  safe  strain 
for  wire  rope,  multiply  the  square  of  the 
circumference  in  inches  by  .3  for  iron, 
and  .8  for  steel  wire.  The  breaking  load 
is  about  three  times  the  safe  load. 

Weight  in  Ibs.  per  fathom  is  equal  to 
the  square  of  the  circumference  in 
inches.  Thus  4-inch  wire  rope  would 
weigh  4X4=16  Ibs.  per  fathom. 


HORSEPOWER. 

Horsepower  is  the  amount  of  mechan- 
ical force  required  to  raise  33,000  pounds 
one  foot  high,  per  minute. 
How  to  Find  Horsepower  of  an  Engine 

Area  of  piston  in  inches,  multiplied  by 
pressure  per  square  inch,  multiplied  by 
speed  of  piston  in  feet  per  minute,  and 
that  product  divided  by  33,000=1  Horse- 
power. 

The  pressure  per  square  inch  should 
be  the  mean  effective  pressure  through- 
out the  stroke  exerted  on  the  piston, 
which  can  be  found  by  attaching  an  indi- 
cator to  the  engine.  The  result  will  then 
be  what  engineers  term  indicated  Horse- 
power. 

The  Horsepower  of  bojlers  is  best  de- 
fined by. the  heating  surface  of  a  boiler 
and  is  different  according  to  their 
construction.  A  Tubular  Boiler  will 
give  about  one  horsepower  to  every  15 
square  feet  of  heating  surface;  a  Flue 
Boiler  every  12  square  feet,  and  a  Cylin- 
der Boiler  10  square  feet  gives  one  horse- 
power. There  is  no  standard  law  gov- 
erning the  horsepower  of  Steam  Boilers, 
but  this  rule  is  adopted  by  most  experts 
as  'a  fair  rating. 

One  cubic  foot  of  water  evaporated 
per  hour  =  1  nominal  horsepower. 

7%  pounds  of  coal  consumed  per  hour 
will  evaporate  1  cubic  foot  of  water  =  1 
horsepower. 

One  square  foot  of  grate  will  con- 
sume an  average  of  12  pounds  of  coal 
per  hour  =  1  6-10  horsepower. 

A  theoretically  perfect  steam  engine 
consumes  66-100  pounds  of  coal  per  hour 
per  horsepower. 

Marine  condensing  engines  consume 
2  to  6  pounds  of  coal  per  horsepower. 


WIRELESS  COURSE— LESSON  NO.  13 


101 


TABLE   OF   EQUIVALENTS. 
Length. 

1  in. =25.40010  mm. 

1  ft.=0.30480  Meter 

1  yd.=0.91440  Meter 

1  mile  =  1.60935  Km. 

1  Nautical  Mile  =  1853.25  Meters 

1  fathom=  1.829  Meters 

1  Meter=39.37043  In. 

1  Meter=3.28083  Ft. 

1  Meter=  1.09361  Yds. 

1  Km.=0.62137  Mile 

Area. 

1  Sq.  In. =6.452  Sq.  cm. 
1  sq.  ft.=9.290  Sq.  dm. 
1    Sq.    Yd.=0.836   Sq.    M. 
1  Sq.  Mile=259.008  Hectares 
1   Sq.   cm,=0.1550  Sq.   In. 
1   Sq.   M.  =  10.764   Sq.   Ft. 
1  Sq.   M.  =  1.196   Sq.   Yd. 

Weight. 

1  grain=64.7989  mg. 
1  oz.  A v. =28.3495  Gm. 
1  oz.  Troy=31. 10348  Gm. 
1  Ib.  Av. =453.5924  Gm. 
1  Ib.  Troy=0.37324  Kilo. 
1  Ib.   Av.=0.45359   Kilo. 
1  mg.=0.01543  grain. 
1   Gm.  =  15. 43236  grains. 
1  Kilo.=33.814  flu.  oz. 
1  Kilo.=2.20462  Ib.  Av. 
1  Kilo.=2.67924  Ib.  Troy. 
1  Kilo.  =  35.274  oz.  Av. 
1   Kilo.=32.1507  oz.  Trby. 
1   Millier  or  Tonne=2204.62  Ib.  Av. 
1  Quintal=220.462  Ib.  Av. 

Volume. 

1  minim  (wjater)  =0.06161  c.c. 

1  flu.  dr.=3.70  c.c. 

1  flu.  oz.=29.5737  c.c. 

1  Apoth.  oz.  (water)  =31. 10348  c.c. 

1  quart=0.94636  Liter 

1  U.  S.  gal.=3.78543  Liters 

1  bushel=0.35239  Hectol 

1  c.c.  =  16.23   minims    (water) 

1  c.c.=0.2702  flu.  dr. 

1   Centiliter=0.338    flu.    oz. 

1   Liter=1.0567  qt. 

1   Liter=0.26417  gal. 

1   Decaliter=2.6417  gal. 

1  Hectoliter=2.8377  bushels 

1  cu.  in.  =  16.387  c.c. 

1  cu.  ft.=0.02832  c.  M. 

1  cu.  yd. =0.765  c.  M. 

1  c.c. =0.05102  cu.  in. 

1  c.  dm. =61023  cu.  in. 

1  c.  M. =35.314  cu.  ft. 

1  c.  M.  =  1.308  cu.  yd. 

Force. 

1  Poundal  =  13,825  dynes. 


TABLE    OF    EQUIVALENTS 
(Continued.) 

1   Pound=4.45Xl05  dynes 

1  Grain=63.6  d*ynes 

1  Gram=981  dynes. 

Energy. 

1  foot-pound= 13,823    gram-centimeters 
.    1.3560X107  ergs 

1  foot-poundal=4.214Xl05  ergs 

1  foot-ton=3.096Xl07  gram-centimeters 
3.0374X1010  ergs 

1  joule=107  ergs 

Power,  Energy  Rate,  or  Activity. 

1  horse-power=746  watts 

1  horse-power=7.604Xl06  gm.  cm.  per 
second  7.46X109  ergs  per  second 

1  metric  horse-power=7.5Xl06  gm.  cm. 
per  second  7.36X109  ergs  per  sec- 
ond 

1  kilowatt=1010  ergs  per  second 

1  watt=107  ergs  per  second 

Doubling  the  diameter  of  a  pipe  in- 
creases its  capacity  four  times. 

Double  riveting  is  from  16  to  20  per 
cent,  stronger  than  single. 

One  cubic  foot  of  anthracite  coal 
weighs  53  pounds. 

One  cubic  foot  of  bituminous  coal 
weighs  from  47  to  50  pounds. 

One  ton  of  coal  is  equivalent  to  two 
cords  of  wood  for  steam  purposes. 

A  gallon  of  water  (U.  S.  Standard) 
weighs  8  1-3  pounds  and  contains  231 
cubic  inches. 

There  are  nine  square  feet  of  heating 
surface  to  each  square  foot  of  grate,  sur- 
face. 

A  cubic  foot  of  water  contains  7Vz 
gallons,  1728  cubic  inches,  and  weighs 
62.425  pounds,  at  39.1°  F.  or  59.76  Ib.  at 
212°  F. 

Each  nominal  horsepower  of  a  boiler 
requires  30  to  35  pounds  of  wjater  per 
hour. 


Following  is  a  table  showing  the  safe 
carrying  capacity  of  interior  wires: 

Size  of                     Area  in  Current  in 

wire.  B.  &  S.  Circular  amperes 

No.       «                     Mils.  Rubber  Ins. 

14       4,107  12 

12        6,530  17 

10       10,380  24 

8        16,510  33 

6        26,250  46 

5        33,100  54 

4       41,740  65 

3        52,630  76 

2        66.370  90 

1 83,690  107 

0       105,500  127 

00      133.100  150 

000    167,800  177 


102 


WIRELESS  COURSE— LESSON  NO.  13 


CONNECTING  AND  SOLDERING  WIRES. 

Where  any  joints  between  span  wires  and  lead-in  wires,  or  other  connections 
are  to  be  made,  it  is  of  the  utmost  importance  that  the  surface  of  the  conductor  at  the 
point  of  joining,  shall  be  thoroughly  cleaned,  which  can  be  readily  accomplished  by 
scraping  with  a  knife  or  better  yet,  by  sand-papering  with  sand  or  emery  paper,  until 
the  wire  is  bright  and  shiny. 

This  thorough  cleaning  of  the  wire  is  necessitated  by  the  oxidization  or  corrosive 
coating  forming  on  its  surface,  due  to  certain  oxidizing  elements  in  the  air,  and  if  not 
done,  the  joint  even  though  soldered  is  seldom  what  it  should  be,  notwithstanding 
it  may  have  a  good  appearance. 

As  aforementioned,  "Aluminite"  solder  is  very  excellent  for  use  in  soldering 
aluminum  wires  or  conductors,  as  is  also  the  formula  given  below:  —  Take  an  alloy 
composed  _of  6  parts  aluminum,  2  parts  zinc  and  4  parts  of  phosphor  tin.  For  a 
flux,  stearic  acid  is  employed,  and  the  sluggish  solder  is  pushed  along  the  seams  or 
joints  by  means  of  an  iron  wire. 

For  soldering  wires  composed  of  copper,  phosphor  bronze  or  brass,  any  standard 
flux  may  be  used,  such  as  the  "Allen"  soldering  stick,  "No-Korode"  paste,  rosin,  etc., 
or  the  following  mixture  recommended  by  the  Fire  Underwriters:  — 

Saturated  solution  of  zinc  chloride  ...........................  5  parts. 

Alcohol    .....................................................  4  parts. 

Glycerine     ......................  .  ............................  1  part. 


IMPROVED    TINNING   ACID. 

,,     .     . 

Muriatic  acid  1  pound;  put  into  it  all 

the  zinc  it  will  dissolve,  and  1  ounce  of 
sal  ammoniac,   then  it  is  ready  for  use. 


FLUXES    FOR   SOLDERING   OR 

WELDING. 

~  ,   „  ~  ,    . 

Copper  and  Brass  ........  Sal-Ammomac 


COMPOSITION  OF  SOLDERS. 

Fine  Solder  is  an  alloy  of  two  parts 
of  block  tin,  and  one  part  of  lead. 
Glazing  solder  is  equal  parts  of  block  tin 
and  lead.  Plumbing  solder,  one  part 
block  tin;  two  parts  lead. 


T)  .i 

Lead  ...................  Tallow  or  Resin 

Lead  and  Tin  Pipes 

Resin  and  Sweet  Oil 
Tinned   Iron    .....................  Resin 

Zinc    ..................  Chloride  of  Zinc 

Steel:  Pulverize  together  1  part  sal- 
ammoniac  and  10  parts  of  borax  and 
fuse  until  clear.  When  solidified,  pul- 
verize to  powder. 


Muriatic  acid  should  not  be  used  for  soldering  any  electrical  connections  what- 
ever, as  it  causes  the  joint  to  corrode  in  a  short  time. 

To  accomplish  the  soldering  of  a  good  joint,  does  not  require  any  great  amount 
of  skill,  providing  the  joint  is  well  heated  by  means  of  a  blow  torch  or  soldering  copper, 
the  flux  applied,  and  the  solder  fed  into  the  joint  until  the  whole  juncture  is  thoroughly 
permeated  with  molten  soldei  and  it  starts  to  run. 

If  any  difficulty  is  experienced  in  tinning  the  end  of  the  soldering  copper,  or 
iron  as  it  is  called,  it  may  be  quickly  cleaned  and  tinned  while  hot,  by  rubbing  it  in 
sal-ammoniac  and  then  smearing  solder  on  it.  If  the  copper  becomes  roughened  or 
burned  on  its  face,  it  should  be  ground  or  filed  smooth. 

To  give  an  idea  to  the  unitiated,  as  to  the  method  pursued  in  forming  a  wire 
joint,  the  following  drawings  (figs.  39  to  42)  will  serve.  They  explain  themselves,  and 


Fig.  39 

it  may  be  said,  that  all  such  joints  are  supposed  to  be  mechanically  and  electrically 
perfect,  before  soldering.  This  is  done  to  preserve  the  conductivity  of  the  joint,  other- 
wise oxidization  soon  sets  in,  and  in  a  short  while,  the  resistance  of  the  joint  ;s  several 
times  its  original  value,  which  proves  too  much  of  an  obstacle  for  the  feeble  aerial 
currents  to  surmount,  giving  rise  to  the  supposed  deterioration  of  the  instruments,  which 
is  seldom  the  case. 


WIRELESS  COURSE— LESSON  NO.  13 


Fig.  40 


Fig.  41 


AERIAL  LEAD-IN 

J°INT'  © 


4 


104 


WIRELESS  COURSE— LESSON  NO.  13 


T 

LOW 

PRESSURE 
f       LOW      \ 

WOLTAGE; 


yj 


§« 


II 

(DO 


I 


Qa 

!$ 

1 
| 

= 

jz3-                 -^ 

VSMALLPIPE  IN 
(HIGH  RESIS.)! 

i 

:?X] 

M 

r^ 

ii 

MODERATE  FLOW  VERY  SMALL  FLOW 

OF  WATE R        '    ,        OF  WATER 
(MEDIUM  AMPERAGE)    (VERY  LOWAMPERAGE 

The  Electrical  Units  are  as  follows: 

Volt. — The  Unit  of  Electro  Motive 
Force — force  required  to  send  one 
ampere  of  current  through  one  ohm 
of  resistance. 

Ohm. — Unit  of  Resistance — the  resist- 
ance offered  to  the  passage  of  one 
ampere  impelled  by  one  volt. 

Ampere. — Unit  of  Current — the  current 
which  one  volt  can  send  through  a 
resistance  of  one  ohm. 

Coulomb. — Unit  of  Quantity — quantity 
of  current,  which,  impelled  by  one 
volt,  would  pass  through  one  ohm 
in  one  second. 

Farad. — Unit  of  Capacity — the  capacity 
of  a  conductor  or  condenser  which 
will  hold  one  coulomb  under  the 
pressure  of  one  volt. 

The  Henry=The  practical  unit  of  induct- 
ance. 

Watt. — Unit  of  Power — the  power  to  do 
work  when  one  ampere  passes 
through  one  ohm  under  pressure  or 
one  volt;  746  Watts  equal  one  horse- 
power. 

Joule. — Unit  of  Work — the  work  done 
by  one  watt  in  ope  second. 


t))f))jjjjjjjfjjjj'j 


The  greater  the  electro-motive  force,  the 

greater  the  results. 

The  current  strength  is  directly  pro- 
portional to  the  volts,  and  inversely 
proportional  to  the  ohms.  This  is 
Ohm's  Law,  and  expresses  the  rela- 
tion which  the  three  units  bear  to 
each  other. 

The  amperes  are  equal  to  the  volts 
divided  by  the  ohms. 
Also  the  volts  are  equal  to  the  am- 
peres multiplied  by  the  ohms. 

The   ohms  are   equal  to   the  volts 
divided  by  the  amperes. 


1st. 


2d. 


3d. 


rr 
ii 


LARGE    FLOW 
OF  WATER 
(HIGH  AMPERAGE) 


SMALL    FLOW 
OF  WATER    v 

(LOW  AMPERAGE) 


WIRELESS    COURSE— LESSON    NO.    14 


105 


Lesson  Number  Fourteen. 

OPERATION    OF    THE    INSTRUMENTS— WIRELESS    REGULATIONS. 

<— rHE  operation  and  tuning  of  the  instruments  in  wireless  circuits  is  more  or  les.> 
/fl      complicated,  the  adjustment  of  one  having  a  certain   effect   on  the  others,   el, 
^In  untuned  wireless   telegraph   circuits,   the  operation   is   of   course   quite   simple, 
and  mav  be  readily  understood  from  the  diagram  fig.  1,  which  shows  the  connections 
of  a  spark  coil,  battery,  key  and  spark  gap  at  the  transmitting  station;   and  an   auio 
coherer  detector,  battery  and  telephone  receiver  at  the  receiving  end. 


B-  SATTEFTY 

SC- SPARK  Coiu (4 ) 


s.- 


Fig.  1 


(Courtesy  "Modern  Electrics.") 


Fig.  2 


The  action  of  the  apparatus  is  as  follows:  when  the  sending  key  K,  is  pressed  or 
closed,  the  battery  current  is  circulated  through  the  low  potential  winding  on  the  spark 
coil.  This  coil,  by  means  of  its  high  voltage  or  secondary  winding,  steps  up  the 
voltage  to  a  sufficient  value  to  leap  an  air  space  in  the  spark  gap,  S  G,  which  results 
in  the  aerial  wires  A,  and  ground  G,  becoming  charged.  These  charged  arms  of  the 
open  oscillating  circuit,  as  it  is  termed,  set  up  electro-magnetic  waves  in  the  ether, 
the  length  of  the  radiated  wave  being  approximately  4  (or  nearer  4.5)  times  the 
length  of  the  aerial  wire,  from  its  outer  end  to  the  spark  gap. 

The  waves  thus  set  up  in  the  ether,  at  the  transmitting  station,  travel  at  the 
marvelous  velocity  of  186,500  miles  per  second,  and  in  the  course  of  their  travels, 
impinge  on  the  receiving  aerial  A,  and  manifest  their  presence,  by  the  setting 
up  of  high  frequency  oscillations  or  currents  in  the  aerial  wire.  These  pass  down 
through  the  detector,  A  C,  to  the  ground  G,  the  action  on  the  detector  being 
noted  by  means  of  the  telephone  receiver  and  battery  shunted  around  it.  Every  time 
a  spark  jumps  the  gap,  S  G.  a  buzzing  sound  is  heard  in  the  telephone  receiver, 
providing  the  detector  is  correctly  adjusted.  The  receiving  set  and  aerial  here 
shown,  will  respond  to  any  wave-length,  if  sufficiently  close  to  the  sending  station, 
but  will  respond  best  to  a  wave-length  approximating  the  value  of  the  natural  period 
of  the  aerial,  when  distant  from  the  sending  station. 

From  the  foregoing  discussion,  it  will  probably  now  be  evident,  that;  if  the  re- 
ceiving station  above  cited,  was  to  receive  from  a  distant  sending  station  radiating  a 
wave  whose  length  did  not  correspond  with  its  own,  it  would  be  necessary  to_  so 
alter  the  receiving  aerial's  length,  that  it  would  have  a  natural  wave-length  equiva- 
lent to  the  sending  station. 

It  would  be  quite  cumbersome  and  awkward  to  be  changing  the  length  of  the 
aerial  wire  to  correspond  with  every  wave-length  which  it  was  desired  to  tune  in 
or  receive,  and  so  the  tuning  coil,  as  the  simplest  wave-length  variator  is  termed, 
is  brought  into  service,  in  the  manner  depicted  by  diagram  fig.  2,  where  the  tuning 
coil  or  inductance  is  represented  by  T,  the  detector  D,  telephone  receivers  R,  battery 
B,  aerial  A,  and  ground  G. 

It  is  easy  to  comprehend  that  if  the  sliding  contact  on  the  tuning  coil  is  movrd 
downward,  as  shown  here,  it  will  artificially  lengthen  the  aerial,  and  vice  versa,  by 
adding  more  or  less  meters  of  wire  to  it,  and  so,  within  the  capacity  of  the  tuning  coil 
and  aerial,  any  desired  wave-length  may  be  adjusted  for,  and  the  open  oscillating  cir- 
cuit through  aerial,  tuning  coil  and  ground,  made  to  oscillate  or  vibrate  in  tune  or 
resonance  with  the  waves  impressed  upon 'it.  When  this  has  been  accomplished  the 
maximum  effect  will  be  exercised  on  the  detector,  and  consequently  on  the  telephone 
receivers. 

Having  gone  over  the  elementary  principles  of  tuning,  the  tuning  of  trans- 
mitting or  sending  stations  will  now  be  taken  up  in  detail. 

Copyright   1912   by   E.   I.   Co. 


106 


WIRELESS  COURSE— LESSON  NO.  14 


The  commonest  type  of  tuned  sending  circuit  is  that  shown  at  fig.  3,  vvnich 
includes  a  single  coil  of  wire  or  helix  H,  for  changing  the  length  of  the  aerial  wire 
and  consequently  the  wave  emitted.  C  is  the  condenser,  S  G,  the  spark  gap,  with 
a  hot  wire  ammeter  added  to  facilitate  the  tuning. 

To  begin  with,  it  will  be  assumed  that,  it  is  desired  to  radiate  a  fairly  long 
wave  or  at  least  one  considerably  longer  than  that  emitted  by  the  aerial  alone.  To 
do  this  the  aerial  slide  should  be  set  to  include  a  good  portion  of  the  helix  turns 
in  series  with  the  aerial  or  the  aerial  slider  must  be  pushed  upward.  Having  done 
this,  the  next  function  to  be  attended  to,  is  that  of  placing  the  condenser  circuit, 
or  closed  oscillating  circuit,  H  C,  S  G,  in  tune  or  resonance,  with  the  open  oscillating 
or  aerial  circuit,  A,  H,  G. 

This  is  done  by  changing  the  position  of  the  movable  condenser  lead  on  the 
helix  H,  and  also  the  capacity  of  the  condenser  C,  until  a  loud  blue-white  spark 
crashes  in  the  gap  S  G,  and  the  hot  wire  ammeter  registers  a  maximum  radiation 
current  in  the  aerial.  The  tuning  may  be  perfected  roughly  by  noting  the  quality 
of  the  _  spark  in  the  gap,  but  this  requires  experience  and  a  common  method  of 
ascertaining  the  degree  of  resonance  attained,  is  to  insert  a  Geissler  tube  or  other 
exhausted  tube  in  the  aerial  lead,  where  the  hot-wire  meter  is  shown  in  the  diagram 
fig.  3.  When  resonance  is  established  the  Geissler  tube  will  glow  the  brightest  and 
vice  versa.  An  anchor  gap  is  also  useful  in  place  of  the  Geissler  tube. 


U 


Fig-  3 


(Courtesy   "Modern   Electrics.")  Fig.  4 


In  the  receiving  tuning  coil,  it  may  be  taken  that  about  four  times  the  length 
of  wire  in  use  on  it,  is  the  increase  in  wave-length  due  to  its  use,  but  for  the  trans- 
mitting helix  no  such  simple  rule  holds  forth. 

There  is  no  simple  method  of  determining  the  wave-length  radiated  from  the  aerial 
of  a  tuned  sending  set,  except  by  the  use  of  a  wave-meter,  which  will  be  treated 
later. 

For  tuned  sending  circuits,  the  wave-length  radiated  can  be  calculated  mathe- 
matically when  the  capacity  and  inductance  of  the  condensers  and  helix  are  definitely 
known. 

This  method  of  finding  the  wave-length  is  given  below;  W  representing  the  wave- 
length in  meters;  TT  =  3.1416  (a  constant);  V,  the  velocity  of  the  wav.es  in  the  ether 
or  300,000,000  meters  per  second;  L,  is  the  inductance  of  those  turns  of  the  helix 
included  in  the  closed  oscillating  circuit,  in  Henries;  C,  is  the  capacity  in  Farads, 
of  the  condenser  used  to  attain  resonance. 

W  —  TT  2  V  V  L  C  ; 

The  inductance  of  the  helix  turns  in  use,  can  be  deduced  from  the  formula  due 
to  L.  Cohen,  as  given  in  the  U.  S.  Bureau  of  Standards  Report,  which  is  as  follows: — 


I,  1  =  39.4787    X  N2 


[ 


The  inductance  L  1,  being  given  in  C.  G.  S.  units,*  which  may  be  transformed  into 
practical  units  or  Henries,  by  dividing  the  inductance  L  1,  by  the  factor  1.000,000,000. 
This  formula  is  accurate  to  within  one-half  of  one  per  cent,  for  any  helix  whose 
length  is  at  least  4  or  5  times  the  diameter.  The  nomenclature  involved  follows: — 
a,  is  the  mean  radius  of  the  helix  in  centimeters,  1,  is  the  length  of  the  helix  in  use, 
in  centimeters,  and  N,  is  the  number  of  turns  of  wire  per  centimeter  of  length. 
The  capacity  of  the  condenser  may.be  calculated  from  the  equation  below: — 


C  = 


2,248  X  K  X  a 
t  X  10,000,000,000 


1,000,000; 


C,  being  the  capacity  in  Farads;  K  the  inductivity  of  dielectric  factor,  which  is  about 
six,   for   common   glass   and    one   for    ordinary   air;    a,    is   the   active   area   in    square 


•Inductance  in  Centimeters. 


WIRELESS  COURSE— LESSON  NO.  14 


107 


inches  of  glass  or  dielectric  coated  on  both  sides  with  charging  plates  and  connected 
on  multiple;  and  t,  is  the  thickness  in  inches  of  the  dielectric  or  insulating  medium. 

Owing  to  the  varying  form  of  differently  constructed  condensers  and  the  brush- 
ing consequent  on  heavy  charges  therein,  the  wave-length  as  calculated  is  a  little 
different  from  that  actually  radiated.  Brushing  from  the  condensers  can  be  largely 
overcome  by  immersing  the  plates  in  oil;  boiled  out  linseed  oil  being  extensively 
used  for  this  purpose. 

So  much  for  the  calculation  of  the  radiated  wave-length.  We  will  now  consider 
the  more  practical  method  utilized  in  commercial  wireless  'work,  viz.,  that  of  using 
a  wave-meter  which  gives  the  value  of  the  radiated  wave  at  once,  the  manner  of 
using  it  being  as  follows: — 

In  fig.  4,  is  outlined  the  sending  circuit  for  a  common  close-coupled  wireless 
station,  and  a  short  distance  from  the  end  of  the  helix  is  shown  the  exciting  loop 
or  coil  of  the  wave-meter  W  M;  the  wave-meter  consisting  of  the  inductance  men- 
tioned, a  variable  condenser,  a  detector  (usually  carborundum),  and  a  pair  of  high 
resistance  telephone  receivers,  shunted  around  the  detector. 

When  the  transmitting  set  has  been  properly  tuned  into  resonance  as  previously 
explained,  the  wave-length  is  determined  by  placing  the  wave-meter  coil  4  to  6  inches, 
or  more,  according  to  the  size  of  the  set,  away  from  the  end  of  the  helix,  or  along- 
side of  it,  as  in  fig.  5,  which  is  advocated  by  many. 


•If 


rmrmrml 


CO-xOCNSCR/ 

AUUI  I  IfMWl, 
'NOlX'AMCt 

Fig.   6 
(Courtesy    "Modern    Electrics.") 


Fig.  5 


In  most  wave-meters,  the  inductance  is  fixed  in  value,  and  the  only  adjustment 
necessary  is  to  vary  the  capacity  of  the  condenser,  until  the  signals  are  heard  the 
loudest  in  the  receivers,  when  the  wave-length  corresponding  to  this  state  of  reso- 
nance in  the  wave-meter  circuit  is  read  directly  from  calibrated  curves  or  tables 
supplied  with  the  meter.  This  is  the  principle  of  all  wave-meters,  the  method  of 
attaining  the  results  being  accomplished  a  little  different  in  some. 

The  Pierce  wave-meter,  for  instance,  employs  a  similar  hook-up  'to  that  shown 
but  has  no  detector,  using  instead,  a  special  high  frequency  wireless  telephone 
receiver,  which  indicates  when  the  maximum  energy  traverses  the  circuit.  The 
Marconi  wave-meter  is  a  very  good  one,  and  utilizes  a  carborundum  detector,  placed 
on  a  shunt  circuit  to  the  main  oscillating  circuit,  as  can  be  seen  from  the  diagram 
fig.  6,  which  arrangement  insures  a  high  accuracy  in  all  of  the  readings  made  by 
it.  The  Marconi  wave-meter  complete  is  depicted  at  fig.  7. 

In  diagram  8,  the  arrangement  for  measuring  the  wave-length  in  loose-coupled 
transmitting  circuits  is  brought  out,  the  wave-meter  coil  being  placed  near  the 
secondary  coil  of  the  oscillation  transformer,  which  is,  of  course,  at  the  same  time 
in  close  proximity  to  the  primary,  but  this  makes  no  difference  as  they  are  in  tune. 

To  transmit  a  certain  definite  wave-length  in  connection  with  a  wave-meter, 
the  meter  should  be  set  for  the  desired  wave,  by  checking  off  from  the  table  accom- 
panying it,  and  then  the  sending  condenser  and  inductance  adjusted  until  the  maximum 
amount  of  energy  passes  through  the  wave-meter  circuit,  made  apparent  by  the 
loudness  of  the  signals  int  the  telephone  receivers.  Of  course,  the  open  and  closed 
oscillating  circuits  must  be  tuned  to  resonance  by  noting  the  spark,  and  the  reading 
of  the  hot-wire  meter  or  the  glow  in  a  resonance  tube. 


108 


WIRELESS  COURSE— LESSON  NO.  14 


The  tuning  of  the  receiving  apparatus  was  explained  partially  at  the  beginning 
of  this  lesson,  i.  e.,  the  philosophy  of  adding  additional  inductance  to  the  aerial  to 
get  the  open  oscillating  circuit  in  tune  with  the  incoming  wave,  and  this  is  one 
of  the  fundamental  factors  in  the  tuning  of  the  receiving  circuit. 

The  most  important  detail  in  the  receiving  circuit,  is  the  detector,  and  a  number 
of  different  ones  are  and  have  been  used.  So-called  crystal  detectors,  or  more 
correctly,,  solid  rectifying  detectors,  are  mostly  in  use  now,  although  the  "Audion," 
a  form  of  gas  detector,  similar  to  the  Fleming  oscillation  valve,  has  been  adopted 
in  many  stations.  The  Marconi  company  uses  the  Fleming  valve,  and  find  it  very 
satisfactory,  especially  in  cases  of  severe  static  or  interference. 

The  detector,  whatever  its  ilk  or  type,  should  be  very  carefully  treated  and 
adjusted,  to  realize  good  efficient  service  from  it.  First,  it  should  be  mounted  upon 
some  shock  absorbing  mat,  such  as  thick  felt,  so  that  anv  outside  jars  or  vibrations 
do  not  reach  it.  Secondly,  the  detector,  except  in  the  case  of  the  valve  or  other 
sealed  types,  is  best  placed  under  an  airtight  cover  of  metal  or  glass  to  prevent 
the  oxidizing  agents  in  the  air,  especially  ozone,  from  attacking  the  crystals,  mate- 
rially lessening  their  efficiency  and  life.  Under  the  cover  placed  over  the  detector, 


Fig.  8 


Fig.  7 
(Courtesy  "Modern   Electrics.") 

should  also  be  placed,  a  small  quantity  of  dry  calcium  chloride,  as  an  air  drier. 
A  metal  cover  over  the  detector  is  preferable,  as  it  tends  to  protect  the  instrument 
from  the  powerful  currents  set  up  by  the  sending  apparatus  in  the  home  station. 

The  detector  is  generally  adjusted  to  its  highest  sensitiveness  by  means  of  a 
test  buzzer,  as  they  are  called,  the  connections  for  it  being  given  __  in  diagram  fig. 
9,  which  also  shows  a  wire  leading  from  the  contact  screw  on  the"  buzzer  or  bell, 


Fig.  9 
(Courtesy  "Modern   Electrics.")  Fig.    10 

to  the  ground  lead,  with  a  push  button  and  battery  for  operating  the  buzzer 
itself.  The  buzzer  should  be  put  in  some  place  away  from  the  receiving  instru- 
ments, so  that  only  the  sound  in  the  receivers  is  heard. 

The  detector  is  adjusted  to  the  proper  degree,  by  varying  the  amount  of  current 
fed  to   it   in   some   types,   employing   a   battery,   or   by   varying   the    tension   existing 


WIRELESS  COURSE— LESSON  NO.   14 


109 


between  the  active  elements,  such  as  the  crystals,  pushing  the  test  buzzer  button  at 
intervals,  to  imitate  dots  and  dashes,  and  when  the  maximum  sensibility  has  been 
reached,  the  buzzing  in  the  telephone  receivers  will  be  loudest,  and  the  detector  is 
then  in  a  state  to  receive  incoming  wireless  signals. 

Where  the  detector  is  located  in  a  sending  and  receiving  station,  it  should  be  guard- 
ed from  the  powerful  waves  set  up  while  sending,  by  shunting  it  with  a  switch  con- 
nected across  it;  the  switch  being  manually  operated,  or  better  automatically  from  the 
sending  key,  by  having  it  arranged  to  work  an  extra  contact  or  a  relay  for  this  pur- 
pose. 

Referring  to  fig.  10,  a  tuned  receiving  set  is  illustrated  diagrammatically,  with  a 
close-coupled  tuning  coil,  a  variable  condenser  or  capacity,  a  fixed  condenser,  four  dif- 
ferent detectors,  a  potentiometer  and  battery  for  the  detectors  requiring  battery  cur- 
rent, and  the  necessary  controlling  switches. 

Here,  the  variable  condenser  is  shown  connected  across  the  whole  winding  on 
the  tuning  coil,  but  it  makes  a  considerable  difference,  if  it  is  inserted  in  the  ground 
lead,  the  first  arrangement  adapting  the  set  to  receive  the  longest  wave-lengths  within 
its  power,  while  when  put  in  series  with  the  ground,  it  renders  the  set  tunable  for 
the  shortest  wave-lengths  within  its  range.  There  are  several  ways  of  connecting  up 
the  variable  condenser,  but  the  two  mentioned  here  are  the  most  common,  where  but 
one  variable  condenser  is  utilized. 

The  fixed  condenser,  by  its  charging  and  discharging  action  tends  to  raise  to  a 
maximum,  the  effects  of  the  oscillations  impressed  upon  the  detector,  and  generall} 
is  found  best  if  of  the  series  type. 

The  battery  switch,  a  two  point  type,  permits  of  placing  the  receivers  in  circuit 
with  the  crystal  detectors  alone  or  in  circuit  with  the  potentiometer,  whose  duty 
is  that  of  regulating  precisely  the  amount  of  voltage  and  current  supplied  to  the 
detectors.  A  non-inductive  form  of  potentiometer  is  always  preferable  to  an  induc- 
tive one,  as  the  inductive  kicks  of  the  coil,  forming  the  inductive  type,  tends  to  make 
false  noises  and  signals  in  the  receivers.  The  graphite  rod  type,  is  quite  excellent  and 
widely  used,  having  a  very  high,  constant  resistance,  easily  adjusted,  besides  being 
positively  non-inductive. 

Having  adjusted  the  detector  to  its  maximum  sensitiveness,  the  receivers  should 
be  held  to  the  ears,  and  the  open  oscillating  circuit  wave-length  varied  by  moving 
the  position  of  'the  ground  slider  or  contact  shown  in  fig.  10,  to  include  more  or 
less  turns  of  the  inductance,  the  more  turns  left  in  circuit,  the  greater  the  equivalent 
wave-length  capacity.  When  the  signals  are  heard  in  the  receivers  best,  after  havinp- 
tuned  roughly  by  moving  the  ground  slider,  the  tuning  may  be  perfected  by  manipu- 
lating the  variable  condenser  and  the  detector  slider.  -Adjusting  the  potentiometer 
will  often  make  some  difference  in  the  strength  of  the  received  signals.  The  variable 
capacity  and  the  ground  slider,  should  be  adjusted  simultaneously  or  nearly  so  for 
the  quickest  tuning. 


Fig.    11  Fig.    12 

(Court esy "_M od e r n    Electrics.") 

The  process  of  tuning  is  essentially  the  same,  for  all  close-coupled  receiving 
systems,  and  but  little  different  for  the  loose-coupled  circuits,  which  are  tuned  as 
follows: 

In  the  case  of  loose-coupled  receiving  transformers,  as  per  diagram  fig.  11,  it  is 
common  to  make  use  of  a  variable  condenser  in  the  ground  wire,  or  across  the  primary 
winding  as  shown,  and  also  of  a  smaller  variable  capacity  shunted  across  the  sec- 
ondary coil,  the  latter  winding  being  preferably  adjustable  as  well  as  the  primary. 
The  cut  given  here,  shows  several  crystal  detectors  connected  to  a  multi-point  switch, 
allowing  any  one  to  be  used  individually. 

In  tuning  such  a  set,  the  secondary  coil  of  the  loose-coupler  is  moved  in  and  out 
of  the  primary  coil,  which  surrounds  it,  with  about  one-half  their  inductances  cut  in. 
When  a  signal  is  heard,  but  not  very  loud,  it  is  necessary  to  adjust  the  capacities  and 
the  inductances,  as  well  as  the  position  of  the  secondary  coil,  until  the  loudest  signals 
are  obtained. 


110 


WIRELESS   COURSE— LESSON   NO.   14 


Such  a  system  .as  just  described,  is  capable  of  eliminating  ordinary  static  or  inter- 
ference, but  for  severe  static  or  power  line  disturbances,  it  is  best  to  adopt  a  looped 
aerial  in  connection  with  a  static  coil  and  variable  capacity  as  depicted  at  hg.  12. 

This  diagram  also  provides  an  extra  wave-length  capacity,  in  the  form  of  a 
variometer,  which  is  nothing  but  two  coils  of  wire,  one  turning  about  its  axis  within 
the  other.  The  static  loop  of  the  aerial  leads  down  through  the  static  inductance  and 
condenser. 

In  tuning  this  circuit,  the  variable  capacity  in  the  loose-coupler  secondary  circuit, 
and  the  position  of  the  secondary  coil  may  be  about  half  cut  in,  and  then  the  vario- 
meter adjusted  until  signals  are  heard  loudest,  when  tuning  may  be  finished  by  adjust- 
ing the  loose-coupler  and  variable  condenser. 

If  now,  any  static  or  interference  occurs,  it  can  generally  be  eliminated  by  the 
proper  regulating  of  the  static  coil  and  the  variable  condenser  connected  with  it. 

For  severe  and  unmanageable  cases  of  static  or  interference,  use  should  be  made 
of  the  "Fessenden"  or  "Marconi"  interference  preventers,  both  of  which  were  dia- 
grammed in  the  section  on  "Hook-Ups." 


In  general,  the  operator  will  find  it  necessary  to  learn  the  best  manner  in  which 
to  tune  in  a  certain  set  of  apparatus  by  actual  experience  and  trying  out. 

In  cut  No.  13,  is  shown  the  Doenitz  Wave-meter.  The  condenser  is  composed 
of  48  plates,  with  a  radius  of  100  millimeters,  and  a  thickness  of  one  millimeter.  The 
plates  are  semi-circular,  and  24  of  them  are  arranged  2  to  3  millimeters  apart  in  a  verti- 


Fig.    14 


cal  plane;  the  other  24  plates  having  the  same  spacing  and  attached  to  a  shaft  or 
spindle,  provided  with  an  adjusting  rotary  knob.  By  turning  the  knob,  the  moving 
plates  are  interposed  between  the  stationary  plates,  to  increase  or  decrease  the  capacity 
as  desired.  The  whole  condenser  is  placed  in  a  receptacle  containing  oil. 


WIRELESS   COURSE— LESSON   NO.   14 


111 


The  apparatus  is  provided  with  a  self-inductance  spiral.  In  using  the  wave-meter, 
it  is  placed  in  close  proximity  to  the  transmitting  set,  whose  wave-length  is  to  be  as- 
certained, in  such  a  manner  that  the  self-inductance  spiral  is  parallel  to  the  sending 
helix  turns. 

In  cut    No.  14,  is   depicted  a   tuner,  having  a   variable  condenser    in  the  base  K. 


Fig.  15 

^»  -j 

The  coil  S  P  P,  is  the  primary,  while  coil  S  P  S,  is  the  secondary.  Variation  of  the 
tuning  condenser  is  effected  by  moving  the  arm  G  L.  An  auxiliary  secondary  coil 
is  shown  at  left  of  figure. 

At  fig.  15,  is  illustrated  a  complete  Telefunken  station,  with  one  sending  and  two 
receiving  sets  of  instruments.  One  receiving  set  is  composed  of  an  electrolytic  de- 
tector and  telephone  receiver,  while  the  other  comprises  the  coherer  and  a  Morse  tape- 
register.  In  the  sending  set,  is  utilized  a  mercury  interrupter  and  open  core  trans- 
'irmer,  with  tuning  inductance. 


112  WIRELESS   COURSE— LESSON  NO.   14. 

WIRELESS  REGULATIONS.* 


NORMAL  WAVE  LENGTH. 

First.  Every  station  shall  be  required  to  designate  a  certain  definite  wave 
length  as  the  normal  sending  and  receiving  wave  length  of  the  station.  This  wave 
length  shall  not  exceed  six  hundred  meters  or  it  shall  exceed  one  thousand  six  hun- 
dred meters.  Every  coastal  station  open  to  general  public  service  shall  at  all  times 
be  ready  to  receive  messages  of  such  wave  lengths  as  are  required  by  the  Berlin  con- 
vention. Every  ship  station,  except  as  hereinafter  provided,  and  every  coast  station 
open  to  general  public  service  shall  be  prepared  to  use  two  sending  wave  lengths, 
one  of  three  hundred  meters  and  one  of  six  hundred  meters,  as  required  by  the  inter- 
nation?.!  convention  in  force:  Provided,  That  the  Secretary  of  Commerce  and  Labor 
may,  in  his  discretion,  change  the  limit  of  wave  length  reservation  made  by  regula- 
tions first  and  second  to  accord  with  any  international  agreement  to  which  the 
United  States  is  a  party. 

OTHER  WAVE   LENGTHS. 

Second.  In  addition  to  the  normal  sending  wave  length  all  stations,  except  as 
provided  hereinafter  in  these  regulations,  may  use  other  sending  wave  lengths: 
Provided,  That  they  do  not  exceed  six  hundred  meters  or  that  they  do  exceed  one 
thousand  six  hundred  meters:  Provided  further,  That  the  character  of  the  waves 
emitted  conforms  to  the  requirements  of  regulations  third  and  fourth  following. 

USE  OF  A  "PURE  WAVE." 

Third.  At  all  stations  if  the  sending  apparatus,  to  be  referred  to  hereinafter 
as  the  "transmitter,"  is  of  such  a  character  that  the  energy  is  radiated  in  two  or 
more  wave  lengths,  more  or  less  sharply  defined,  as  indicated  by  a  sensitive  wave 
meter,  the  energy  in  no  one  of  the  lesser  waves  shall  exceed  ten  per  centum  of  that 
in  the  greatest. 

USE   OF  A  "SHARP  WAVE." 

Fourth.     At  all  stations  the  logarithmic'  decrement  per  complete  oscillation  in  the 
wave    trains    emitted    by    the    transmitter    shall    not    exceed    two-tenths,    except    when 
sending  distress   signals  or   signals   and   messages   relating  thereto. 
USE   OF  "STANDARD   DISTRESS   WAVE." 

Fifth.  Every  station  on  shipboard  shall  be  prepared  to  send  distress  calls  on 
the  normal  wave  length  designated  by  the  international  convention  in  force,  except 
on  vessels  of  small  tonnage  unable  to  have  plants  insuring  that  wave  length. 

SIGNAL  OF  DISTRESS. 

Sixth.     The  distress  call  used  shall  be  the  international  signal  of  distress     .     .     . 

USE  OF  "BROAD  INTERFERING  WAVE"  FOR  DISTRESS   SIGNALS. 

Seventh.  When  sending  distress  signals,  the  transmitter  of  a  station  on  ship- 
board may  be  tuned  in  such  a  manner  as  to  create  a  miximum  of  interference  with  a 
maximum  of  radiation. 

DISTANCE    REQUIREMENT    FOR    DISTRESS    SIGNALS. 

Eighth.  Every  station  orj,  shipboard,  wherever  practicable,  shall  be  prepared  to 
send  distress  signals  of  the  character  specified  in  regulations  fifth  and  sixth  with 
sufficient  power  to  enable  them  to  be  received  by  day  over  sea  a  distance  of  one  hun- 
dred nautical  miles  by  a  shipboard  station  equipped  with  apparatus  for  both'  send- 
ing and  receiving  equal  in  all  essential  particulars  to  that  of  the  station  first  men- 
tioned. 

"RIGHT   OF  WAY"   FO&   DISTRESS    SIGNALS.- 

Ninth.  All  stations  are  required  to  give  absolute  priority  to  signals  and  radio- 
grams relating  to  ships  in  distress;  to  cease  all  sending  on  hearing  a  distress  signal, 
and,  except  when  engaged  in  answering  or  aiding  the  ship  in  distress,  to  refrain 
from  sending  until  all  signals  and  radiograms  relating  thereto  are  completed. 

REDUCED    POWER   FOR    SHIPS    NEAR   A    GOVERNMENT    STATION. 

Tenth.  No  station  on  shipboard,  when  within  fifteen  nautical  miles  of  a  naval  or 
military  station,  shall  use  a  transformer  input  exceeding  one  kilowatt,  nor,  when 
within  five  nautical  miles  of  such  a  station,  a  transformer  not  exceeding  one-half 
kilowatt,  except  for  sending  signals  of  distress  or  signals  or  radiograms  relating  thereto. 

INTERCOMMUNICATION. 

Eleventh.  Each  shore  station  open  to  general  public  service  between  the  coast 
and  vessels  at  sea  shall  be  bound  to  exchange  radiograms  with  any  similar  shore 
station  and  with  any  ship  station  without  distinction  of  the  radio  systems  adopted  by 
such  stations,  respectively,  and  each  station  on  shipboard  shall  be  bound  to  exchange 
radiograms  with  any  other  station  on  shipboard  without  distinction  of  the  radio  sys- 
tems adopted  by  each  station,  respectively. 

It  shall  be  the  duty  of  each  such  shore  station,  during  the  hours  it  is  in  opera- 
tion, to  listen  in  at  intervals  of  not  less  than  fifteen  minutes  and  for  a  period  not  less 
than  two  minutes,  with  the  receiver  tuned  to  receive  messages  of  three  hundred  meter 
wave  lengths. 

See  Wiretes'S  Law.  Lesson  No.  15. 


*Principal  Reputations  as  given  in  new  Wireless  Law.  effective  since  Dec.  13,  1912.     S-6412. 


WIRELESS   COURSE— LESSON    NO.   15 


113 


Lesson  Number  Fifteen. 


LEARNING  TO  OPERATE.— THE  CODES.— THE  WIRELESS  LAW. 

~|N  the  wireless  telegraph,  contrary  to  the  wireless  telephone  which  transmits 
41  speech  wirelessly,  it  is  necessary  to  learn  the  code  of  signals  employed  in  trans- 
*z*  mitting  and  receiving  messages. 

The  code  is  a  series  of  dots  and  dashes,  as  they  are  called,  composed  ot  snort  and 
long  sparks  as  liberated  at  the  sending  station,  a  certain  combination  of  short  and 
!  m"-  sparks  forming  a  code  letter  or  figure.  As  an  example,  suppose  it  is  desired 
to  transmit  the  letter  A,  in  the  Morse  code  of  signals.  This  requires  that  the  sending 
key  be  closed  or  depressed  for  an  instant;  released,  and  again  depressed  for  a  period 
slightly  longer,  the  signals  sent  thus,  being  known  as,  Dot-Space-Dash;  or  a  short 
spark,  no  spark,  long  spark.  Electro-magnetic  waves  corresponding  to  the  short  and 
long  sparks  set  up  at  the  sending  station,  are  propagated  through  the  ether,  to  the 
receiving  station,  where  they  manifest  their  presence,  by  short  and  long  buzzes  in  the 
receivers,  the  various  combinations  being  interpreted  by  the  receiving  operator. 

There  are  three  codes  in  general  use  now,  for  wireless  communication,  viz.:  the 
Morse,  Continental  and  Navy  codes;  the  equivalent  dots  and  dashes  for  letters  and 
figures  in  each  code  appearing  on  next  page. 

There  are  several  different  ways  of  learning  the  codes  so  as  to  operate  properly 
by  them,  and  in  general,  two  classes  of  beginners  in  wireless  undertake  the  work, 
namely,  former  wire  operators,  whom  are  used  to  sounder  Morse,  with  its  back-kick; 
and  the  novice  who  cannot  send  a  dot. 

It  seems  to  be  the  common  experience, 'that  a  wire  operator  taking  up  wireless, 
has  but  little  difficulty  in  grasping  the  rudiments  of  the  newer  art  and  quickly  becom- 
ing an  expert  at  the  wireless  key;  on  the  other  hand,  many  otherwise  well  grounded 
students  of  wireless,  who  think  they  can  operate,  succeed  in  charging  the  ether  with 
a  nondescript  series  of  spasmodic  signals  intended  for  the  code,  which  are  enough  to 
make  good  old  S.  F.  B.  Morse  himself  turn  over  in  anguish. 

The  first  thing  an  operator  must  or  should  learn,  is  the  correct  manner  of  holding 
the  key  in  transmitting,  this  being  very  important,  when  any  long  messages  or  a  batch 
of  them  are  to  be  sent  in  succession. 

A  form  of  grasping  the  key  adopted  by  the  majority  of  fast  commercial  operators, 
is  to  rest  the  first  and  second  fingers  on  the  top  of  the  key  button  and  close  to  the 
edge  of  it,  with  the  thumb  placed  against  the  edge  of  the  button,  see  fig.  1.  Then  the 
first  and  second  fingers  are  curved  to  form  a  quadrant  of  a  circle,  avoiding  any  undue 
straightness  or  rigidity  of  these  fingers  and  the  thumb.  The  third  and  fourth  fingers 
are  partly  closed,  and  the  elbow  allowed  to  rest  easily  upon  the  table,  permitting  the 
wrist  to  be  perfectly  limber.  A  moderately  firm  grasp  should  be  taken  on  the  key,  but 
not  a  rigid  one.  If  the  key  button  is  grasped  too  tightly,  the  hand  will  soon  become 
tired  or  fatigued,  resulting  in  what  is  known  as  "telegrapher's  cramp."  A  little  prac- 
tice, on  the  key,  with  careful  attention  to  the  codes,  will  soon  break  in  the  amateur 
operator,  and  do  more  for  him  than  a  dozen  pages  of  reading  on  the  subject. 


Fig.  1 

In  this  connection  it  might  be  mentioned  that  there  are  on  the  market,  several 
automatic  instruments  which  send  dots  and  dashes  of  regular  length,  irrespective  of 
the  operator's  characteristics,  two  of  them  being  the  "Mecograph"  and  the  "Vibro- 
plex."  These  instruments  are  satisfactory  for  wireless  work,  but  generally  have  to 
be  utilized  in  connection  with  a  relay,  as  they  are  not  capable  of  handling  heavy  cur- 
rents, such  as  occur  in  a  wireless  station  of  any  size.  These  patent  keys  are  operated 
by  a  sidewise  motion,  and  are  claimed  to  prevent  "telegrapher's  cramp,"  but  they 


Copyright   1911'   by   E.   I.    Co. 


114 


WIRELESS   COURSE— LESSON    NO. 

WIRELESS    CODES 


15 


LETTERS 

MORSE 

CONTINENTAL 

NAVY 

A 

o  •• 

•  mm 

••  •• 

B 

•••_•_• 

«•_•_•.._• 

mm  •  •  mm 

c 

•  •    • 

••   •  IM  « 

•  mm  • 

D 

•B  •  • 

•1   •   • 

IB  ••  •• 

P 

• 

• 

•  •• 

F 

•  mm  • 

•  •  mm  • 

mm  mm  mm  • 

Q 

mm  mm  • 

§•_••_• 

••  ••  •  • 

* 

•  •  •  • 

•_•_•_• 

•  •§  •§ 

I 

•  • 

•  • 

• 

J 

mm  •  mm  • 

•  mm  mm  mm 

•  ••  •§  mm 

K 

••  •  •• 

mm_a_mm 

'mm_Jm_mm_m_ 

L 

••• 

•  mm  •  • 

mm_mm_m_ 

M 

••  mM 

Hi  •• 

•  mm  mm  • 

N 

mm  • 

••   • 

•  • 

0 

• 

•i  mm  mm 

•i  • 

P 

•  •  •  • 

•  mm  mm  • 

m_mm_m_mm 

Q 

OH! 

mm_mm_j±_mm_ 

•  mm  •  • 

R 

•  • 

•  ••  • 

•nn 

s 

•  • 

•  •  • 

••_•_•• 

T 

m 

•• 

•• 

u 

•  mm 

•  •  •• 

•  •  mm 

V 

•  •  mm 

•  •  •  mm 

•  mm  mm  mm 

w 

MM  mm 

9_mm_mm 

•  •  mm  • 

x 

!•_•_• 

mm  •  •  mm 

••_:•_•_•• 

Y 

•     0  • 

mm  •  HI  •• 

•  •  • 

Z 

•  •     • 

mmmm  •  • 

•B  ••  ••  mm 

& 

•     •  •  • 

31 

•  ™J*%    - 

•jmm_,mm~mmmm_ 

•  •  •  • 

3 

•  ••••• 

•  •••§•§ 

•_•_•_•• 

* 

•  ••••• 

•_•_•_•_•• 

•LBUH-JI 

•     A    •••    •• 

_B_ 

•  ••••• 

•••••• 

7 

!•_!•_•_• 

•§•§••• 

•B_JLJL_t 

Q^ 

§••••• 

••  •§  ••  •  • 

mm  •  •  •• 

•i  mm  mm  mm  • 

•_••_••_• 

••    A     A    •• 

L 

* 

^  ^" 

•  mm  •  mm  •  • 

$ 

^•••i  •  • 

••  •••••• 

mm  •  •  mm  • 

•  •  mm  mm  •  • 

ABBREVIATED  NUMERALS  USED  BY  CONTINENTAL  OPERATORS. 

1     •mm             2  •  •  •»        3  •  •  •  ••  4-  •  •  «  •  ••    g  • 
6     •••••7«i«B«»«8M«»     9    "a  «     1O    mm- 

WIRELESS  ABBREVIATIONS'. 
G.  E.  -  GOOD  EVENI  NG         4-  -  PLEASE  START  ME.WHERE 

G.  N.-          »•»        NIGHT                      1  3  -  UNDERSTAND 
G.M.-           ^       MORNING              25  -AM   BUSY   NOW 
G.A.-    GO   AHEAD                             3O-NO  MORE 
O.S.-    SHIP  REPORT                      73-  BEST  REGARDS 
D.H.-    FREE  MESSAGE                 TT-  MESSAGE    FOR  VOU 
M.S.G.-  MESSAGE                                32-  DELIVERED 
O.P.R.-  OPERATOR                           99  -KEEP    OUT 
-DISTRESS    SIGNALS* 
SOS         MORSE                     C.Q.D.    CONTINENTAL 

WIRELESS   COURSE— LESSON   NO.    15 


115 


nevertheless  require  as  many  movements  of  the  hand  as  a  common  Morse  key,  in 
sending,  excepting  dot  letters.  Sending  machines  or  keys  must  also  be  kept  in  the 
very  best  condition,  and  carefully  watched,  or  they  become  irregular  in  the  closing  of 
the  contacting  parts,  owing  to  collections  of  oil  and  dirt  or  burnt  surfaces. 

The  Morse  code  in  its  present  form  was  arranged  by  Mr.  Alfred  Vail,  of  Morris- 
town,  N.  J.,  and  due  respect  has  been  given  to  the  most  frequently  occurring  letters,  so 
that  they  may  be  the  shortest. 

CO/L. 


BAT. 


Fig.  2 


The  great  fundamental  building  block  of  a  good  code  sender,  is  the  correct  time 
spacing  of  the  various  signals  employed,  and  composing  the  alphabet.  To  begin  with, 
the  time  unit  upon  which  the  code  is  built,  is  the  dot,  the  shortest  signal  used,  and 
whatever  its  time  duration,  the  spaces  and  dashes  must  be  made  of  proportionate 
length.  This  is  quite  clearly  remembered,  if  it  is  known  that  the  ordinary  space  is 
of  the  same  time  duration  as  a  dot,  and  the  ordinary  dash  twice  the  length  of  a  dot. 
In  the  Morse  code,  the  letter  L,  is  a  dash  of  four  times  the  duration  of  a  dot,  while 
for  the  figure  0,  the  signal  is  an  extra  long  dash,  equivalent  to  the  duration  of  five 
dots.  Between  words,  the  space  interval  should  be  two  ordinary  spaces,  and  between 
sentences,  the  equivalent  of  three  spaces. 

If  the  operator  aspirant  desires  to  be  thoroughly  proficient  >in  his  chosen  pro- 
fession, he  must  pay  the  strictest  attention  to  the  proper  time  spacing  of  the  various 
letters  and  figures  of  the  code.  A  good  plan  for  the  beginner,  is  to  have  a  friend' 
a  short  distance  from  his  place,  who  will  send  arbitrary  signals  to  him,  and  he  will 
undoubtedly  learn  to  receive  quicker  in  this  manner  than  in  any  other,  unless  he  can 
attend  a  school  for  the  purpose. 

Failing  these  facilities,  for  mastering  the  code,  a  very  good  scheme  for  isolated 
students  is  to  employ  a  buzzer  set,  which  includes  a  key  and  battery  as  shown  in  fig. 
2,  placing  the  buzzer  quite  a  distance  from  the  receivers,  so  that  its  armature  noise 


OMNIGRAPHS. 

cannot  be  heard.  From  across  the  armature  and  contact  screw  as  illustrated,  two 
leads  are  taken  to  a  coil  of  wire  (6  turns  are  sufficient),  and  the  shunting  of  different 
lengths  of  this  coil  will  faithfully  imitate  nearby  and  distant  wireless  signals,  the 
tone  of  the  buzz  heard  in  the  receivers  depending  upon  the  thinness  of  the  buzzer 
armature  anrl  also  upon  its  speed  of  vibration.  A  "skeeter"  spark,  as  it  is  often  termed 


116 


WIRELESS   COURSE— LESSON   NO. 


in  the  profession,  meaning  a  "singing"  or  high  pitched  spark  note,  may  be  closely 
imitated  by  altering  the  buzzer  construction  somewhat,  as  shown  at  fig.  3,  and  placing 
a  thin  iron  strip  across  the  magnet  poles,  slightly  above  them,  varying  its  tension 
by  a  thumb  nut  attached  to  one  end  of  it.  This  arrangement  gives  an  exceedingly  high 
note  in  the  receivers. 

The  buzzer  set  described  above  can  be  operated  manually  by  hand,  but  for 
beginners  who  find  it  hard  to  properly  space  the  signals,  it  is  better  to  control  it  from 
some  sort  of  automatic  sending  device,  such  as  the  "Omnigraph,"  •  which  costs  from 
$2.00  up,  according  to  how  elaborate  an  instrument  is  desired.  It  works  on  the  prin- 
ciple, that  a  circular  metal  disc  with  projecting  teeth  around  its  periphery,  and  rotating 
by  means  of  a  spring  mechanism,  opens  and  closes  an  electrical  circuit,  at  definite 
intervals,  by  means  of  a  spring  contact  pressing  against  certain  teeth  while  rotating. 
Different  discs,  for  various  combinations  of  words  and  phrases  can  be  obtained  for 
it,  and  where  the  learner  has  access  to  no  other  teacher,  this  automatic  sender,  capable 
of  transmitting  at  any  speed,  should  be  a  boon. 


Fig.  3 


On  regular  wire  telegraph  land  systems,  a  speed  of  40  to  50  words  per  minute 
is  usual  in  sending,  except  in  bad  weather  it  may  be  reduced  to  25  or  30  or  less.  The 
speed  of  transmission  for  wireless  work,  is  often  as  high  as  40  or  more  words  per 
minute  under  good  conditions,  but  the  United  States  Examiners,  before  whom  all  com- 
mercial ship  operators  must  appear,  require  a  sending  and  receiving  speed  of  not  less 
than  15  words  a  minute,  American  Morse,  or  twelve  words  in  the  Continental  code, 
as  the  operator  may  elect. 

The  Continental  code,  although  recognized  at  the  Berlin  convention  for  Inter- 
national wireless  arrangements,  has  not  been  used  to  any  great  extent  commercially, 
although  the  United  States  Navy  employs  it.  The  advantage  of  the  Continental  code 
over  the  regular  Morse  code,  is  that  there  are  no  spaced  letters,  as  the  letters  O 
and  R,  in  Morse;  the  Continental  signals  bei.ig  composed  of  straight  combinations 
of  dots  and  dashes. 

The  disadvantage  of  the  Continental  code,  when  compared  to  the  Morse,  is  that 
the  figure  symbols  in  the  former,  are  unduly  long  and  requir^  too  much  time  to  send. 
In  the  letter  section  of  the  codes,  there  are  but  few  differences. 

It  is  advisable  for  the  beginner  to  practice  certain  exercises  involving  the  repeti- 
tion of  letters  of  the  same  make-up,  as  dot  letters  and  dash  letters,  etc. 

An  exercise  in  dot  letters  for  the  Morse  code  is: — Ship,  she,  his,  hips,  sips,  pies, 
sheep,  pipe. 

Some  practice  words,  containing  dot  and  dash  letters  are: — Spanish,  spite,  ship- 
shape, dishevel,  dapple,  hissing. 

Some  dash  letters  for  practice  are: — Met,  till,  time,  metal,  pellmell,  mammal,  tittle, 
timid,  skilled,  multiple,  multitude,  mallet,  emit. 

Dot  before  dash  letters: — Awe,  awful,  law,  valve,  Eva,  vault,  lava,  pawl,  squaw. 

Dash  before  dot  letters: — Bend,  bidden,  ban,  dunned,  dabble,  nab,  dined. 

Combination  of  the  last  two: — Julep,  jungle,  quaff,  quake,  exit,  exquisite,  exhaust, 

An  exercise  in  spaced  letters  is: — Err,  errant,  corner,  eczema,  corollary,  co-operate, 
coon,  circus,  buzzard,  correlate,  corrupt,  cohesion,  road,  dory,  there  is  no  royal  road 
to  learning. 

In  learning  the  beginner  should  try  to  send  at  an  even  regular  speed,  going  slow 
at  first  and  gradually  increasing  the  speed -to  the  necessary  degree.  One  of  the  most 
common  defects  in  a  beginner  is  his  choppy  or  irregular  speed  in  transmitting,  which 
makes  it  very  difficult  for  even  a  good  operator  to  receive. 


WIRELESS   COURSE— LESSON   NO.    15  117 

A  large  amount  of  sending  is  easily  and  readily  taken  care  of  by  the  steady  sender, 
who  makes  few  mistakes,  with  consequent  few  repeats,  although  in  long  dispatches 
the  question  sign  should  be  given  after  every  20  words,  which  will  save  repeating  a 
whole  message.  A  steady,  well  trained  sender,  can  operate  for  10  hours  at  a  stretch, 
if  need  be,  but  a  poor  sender,  who  has  not  learned  to  handle  the  key  properly,  would 
succumb  to  a  cramp  in  a  few  hours. 

A  beginner,  or  "ham"  operator  as  they  are  termed  in  popular  parlance,  is  generally 
known  by  his  style  of  sending,  a  very  frequent  fault  of  his  being,  the  string  of  8  or 
10  dots  he  sends  out  like  so  many  shots  from  a  gatling  gun,  and  intended  for  the  poor 
little  letter  P.  It  is  interesting  to  note  in  this  connection,  that  there  are  professional 
operators,  who  cannot  for  the  life  of  them,  send  those  five  dots  representing  the  letter 
P,  correctly  at  high  speed.  It  seems  to  be  a  freak  of  human  nature.  Another1 
string  of  rapid-fire  dots  often  come  hurtling  through  space  intended  for  the  six  dots, 
representing  the  figure  6.  The  only  remedy  for  these  freaks,  is  to  .thoroughly  practice 
over  and  over  again,  those  particular  balky  symbols,  slowly  at  first,  then  faster  until 
normal  speed  is  attained. 

In  the  Morse  code,  a  common  mistake  is  that  of  prolonging  the  T  dash,  and' 
shortening  the  L  dash.  Another  tendency  is  to  lengthen  the  first  and  last  dots  of 
a  letter;  running  the  spaced  dots  together;  dropping  dots  out  of  some  letters;  running 
letters  of  different  words  together;  making  unintelligible  combinations  of  different 
half-words  and  a  multitude  of  others. 

When  the  student  has  learned  how  to  handle  the  key  properly,  so  that  dots  and 
dashes  of  the  proper  length  are  sent  out,  his  dutres  will  concern  the  proper  handling 
of  dispatches  anj  csages  as  sent  in  regular  commercial  work. 

Before  a  mesc.  ,e  can  be  sent,  it  is  necessary  to  send  out  the  call  of  the  station 
desired  to  communicate  with,  and  at  the  proper  wave-length,  as  the  call  might  be 
sent  out  al  :  the  wrong  wave-length,  and  never  be  acknowledged.  A  book 

published  by  im_  J.  S.  Government  Printing  office,  at  Washington,  D.  C.,  gives  all  the 
calls  for  registered  ships  and  shore  stations,  exclusive  of  private  stations,  which  are 
listed  in  a  special  blue  book  published  each  year  by  the  Modern  Publishing  Co.,  N.  Y. 
City,  including  registry  of  station,  at  25  cents. 

For  instance,  suppose  the  station  wanted:  is  rated  in  the  blue  book  as,  call  B  N  G, 
wave-length  428  meters.  In  this  case,  the  call  should  be  repeated  at  intervals  of  about 
fifteen  seconds,  followed  by  the  call  letters  of  the  station  calling,  allowing  time  for 
acknowledgment  of  call.  It_  is  not  always  possible  to  send  out  the  call  at  the  wave- 
length of  the  called  station,  in  which  event  it  is  necessary  to  send  it  out  at  the  regular 
transmitting  wave-length  and  take  a  chance  on  the  operator  of  the  desired  station 
stumbling  over  it,  while  "listening  in,"  at  various  wave-lengths  or  tunes. 

After  the  called  station  acknowledges  the  call,  and  gives  the  "go  ahead  sign," 
abbreviated  to  G  A,  the  following  arrangement  is  a  standard  one  for  sending  the  mes- 
sage: Send  the  sign  "H  R"  or  "M  S  G,"  meaning  message;  then  give  the  number  of 
message;  the  station's  call;  operator's  sign;  number  of  words,  excluding  address  and 
signature;  date;  route  of  message;  address;  body  of  message;  and  signature. 

Regarding  the  charges  on  bon.rd  ship,  land  wire  charges,  or  both,  they  can  be 
given  after  the  "number  of  words."  For  messages  to  be  forwarded  by  a  certain  land 
line,  the  directions  can  be -indicated  after  "Route  of  message,"  by  the  letter  "W.  U." 
for  Western  Union,  "P.  T."  for  Postal  Telegraph,  etc. 

All  messages  are  not  transmitted  in  regular  form  or  as  they  are  written,  the  serv- 
ices of  a  cipher  code,  special  codes,  and  various  abbreviations  being  widely  used  to 
increase  the  speed  of  transmission,  decrease  the  cost  of  transmitting,  and  thirdly,  to 
preserve  secrecy  in  some  cases. 

In  wireless  work  at  present  a  fair  list  of  standard  abbreviations  have  been  generally 
adapted,  some  of  them  being  given  below. 

ABBREVIATIONS. 

G.  A.;  Go  ahead.  Min-  Minute 

A/T        C        f~^  TT       T->          -«  r  /•  JKllIlj     IV-IIIIUIC. 

M.  b.  G.;  or  H.  R.;  Message  for  you;  or,  Msgr;  Messenger. 

^muSSa&e>  j  Msk:  Mistake. 

P-  ?•'•„ Dead  head  or  free  message.  No;  Number. 

A'   «'  Ship  Report.  Ntg;   Nothing. 

R'  £  RA;   °Perator-  N.  M.;  No  more. 

U  M.;  Good  morning.  O.  K.;  All  right. 

IT.  E.;  Good  evening.  Of's;  Office. 

ft  N^Good  night.  Sig;  Signature. 

5J    S';  K^d?y,"  pd;  Paid. 

M.  N.;  Midnight.  Q.  K.;  Quick 

S-  °VvV1^istress  sJ5nal  (International).  G.'  B.'X.;  Get'better  address 

KX;     or,     B.     K.;     Interference:  Bn;  Been 

break;  Get  out.  TCat.  TWtprv 

WT  T      T  T  r  Jjd  i  •    -Oci'i  itry . 

.  U.;  Western  Union.  Bbl;  Barrel. 

P.  T.;  Postal  Telearraph.  Col;  Collect. 

B.  T.;  Bell  Telephone.  Ck-'check 

P.  R.  B.;     (International),    Express    the  R.  R.;  Repeat, 
desire  to  communicnte  by  means  of  the 
international    signal   code   by  wireless. 
(Continental  Code.) 


118  WIRELESS   COURSE— LESSON   NO.   15 

In  times  of  accident  at  sea,  the  wireless  man  is  the  most  important,  except  the 
captain  possibly,  and  on  his  cool  head  and  resourcefulness  depends  the  saving  of  the 
ship  and  its  people,  in  a  great  measure. 

In  many  cases  of  distress  at  sea  there  may  be  only  a  minor  accident  with  no 
immediate  danger,  such  as  a  broken  down  engine,  or  propeller,  in  which  case  the 
operator  is  usually  told  to  signal  aid,  as  soon  as  possible.  \Vhen  a  collision  or  smash- 
up  has  occurred,  and  the  engine  and  dynamo  room  is  flooded,  the  operator  must  resort 
to  his  storage  batteries,  which  are  generally  installed  on  all  large  ships,  and  should  be 
in  every  ship  wireless  station,  for  emergency  uses. 

In  event  of  immediate  danger  of  sinking,  the  operator  should  send  out  the  Inter- 
national distress  signal,  "S.  O.  S."  at  15  second  intervals,  allowing  a  little  time  to 
elapse  between  signals,  for  acknowledgment,  by  those  who  may  happen  to  catch  the 
signal;  upon  receipt  of  acknowledgment,  the  location  of  the  ship,  trouble,  her. name, 
captain's  name,  number  of  people  on  board,  and  any  further  particulars  necessary, 
should  be  sent.  This  form  is  adaptable  only  for  large  size  stations,  with  suitable 
reserve  power  in  their  batteries.  For  small  equipments  no\t  capable  of  sending  over 
100  miles,  it  is  the  best  plan  when  starting  to  send  the  distress  signal,  to  intersperse 
the  location  of  the  ship,  and  possibly  her  name  call,  as  it  has  occurred  where  a  small 
wireless  set  on  a  ship  calling  for  help,  got  gradually  weaker  and  weaker,  and  by  the 
time  an  acknowledgment  came  in  answer  to  the  "S  O  S"  signal,  the  ship  in  trouble 
could  not  give  her  location  or  anything  else,  reserve  power  failing,  at  the  critical 
moment.  In  such  event,  the  vessels  which  might  have  helped  are  powerless  to  do 
anything,  but  generally  in  these  cases  the  seas  are  scoured  pretty  well,  after  knowing 
that  a  ship  somewhere  out  of  sight  is  in  distress. 

The  ideal  wireless  ship  station  as  regards  life-saving  efficiency,  would  be  one 
having  an  oil  engine  driving  a  dynamo,  in  a  watertight  room,  on  the  upper  deck,  with 
a  g-ood  supply  of  engine  fuel  in  the  operating  room,  or  alongside  of  it.  Any  wireless 
set,  especially  those  without  a  reserve  storage  battery,  are  as  good  as  none,  in  event 
of  the  engine  and  boiler  room  becoming  flooded  or  damaged.  Some  important  rules 
formulated  by  the  U.  S.  Navy  Dept.,  regarding  the  handling  of  commercial  wireless 
messages  by  naval  stations  ashore  and  afloat,  are  given  here,  as  ithey  contain  some 
valuable  information  as  to  the  proper  procedure  in  such  business. 

All  naval  wireless  telegraph  stations,  with  the  following  exceptions,  viz.:  those 
at  the  navy  yards  at  Boston,  New  York,  Philadelphia,  Norfolk,  Puge*t  Sound  and 
Mare  Island,  and  the  naval  stations  at  New  Orleans  and  Yerba  Buena,  San  Francisco, 
will  handle  commercial  messages  under  the  following  conditions: 

(1)  That  no  commercial  station  is  able  to  do  the  work. 

(2)  That  no  expense  is  incurred  by  the  Governmenit  thereby. 

(3)  That  no  money  or  account,  in   connection   with   this  business  is  handled  by 
any  person   in  the  employ  of  the   Navy  Department. 

(4)  That    the    handling   of    the    commercial    messages,    shall    not    interfere    with 
Governmenit  business. 

The  Government  handles  all  commercial  wireless  messages  without  charge,  but 
assumes  no  financial  responsibility  whatever  for  errors,  delays,  or  non-delivery. 
Every  effort  will  be  made,  however,  to  forward  all  messages  accepted  accurately  and 
expeditiously  by  the  best  means  available.  Confirmation  copies  of  commercial 
messages  sent  through  naval  wireless  stations  will  be  sent  only  when  request  is 
made  in  advance,  or  within  thirty  days  after  messages  are  forwarded. 

Messages  of  all  kinds  received  from  ships  at  sea  will  ordinarily  be  forwarded 
by  a  land  wire,  the  land  wire  charges  to  be  collected  at  destination. 

In  case  of  isolated  stations,  such  as  stations  on  Alaskan  Islands  and  in  emer- 
gencies these  messages  will  be  relayed  to  other  wireless  stations  for  further  trans- 
mission if  necessary. 

Position  reports  will  be  forwarded  to  owners  or  agents  by  a  land  wire  when 
request  is  made. 

Messages  received  by  land  wire  at  a  naval  wireless  station  for  a  ship  at  sea  will 
be  forwarded  by  wireless,  when  jthe  ship  comes  within  range.  For  this  reason  ships 
should  ordinarily  communicate  with  wireless  stations  while  passing  along  the  coast, 
giving  their  positions. 

Messages  received  by  a  wireless  station  for  a  ship  which  cannot  be  delivered 
for  any  reasons  will  be  returned  to  the  land  wire  company  from  which  it  was  received. 

The  personnel  of  naval  wireless  stations  are  required  to  keep  the  strictest 
secrecy  in  regard  to  the  contents  of  messages  passing  through  their  stations,  and 
they  are  not  permitted  to  communicate  the  fact  that  a  message  on  any  particular 
subject  has  been  received. 

All  messages  are  kept  on  file,  and  senders  and  addressees  may  obtain  copies  of 
all  messages  as  sent  upon  request. 

A  vessel  wishing  to  communicate  with  a  naval  coast  station  should  commence 
calling  when  about  100  miles  from  the  station,  having  first  "listened  in,"  to  ascertain 
that  sh,e  is  not  interfering  with  messages  being  exchanged  within  her  range.  The 
power  and  range  of  many  stations,  however,  are  being  rapidly  increased,  and  vessels 
should  note  at  what  distances  they  hear  certain  stations  working  with  merchant 
ships  in  order  that  communication  may  be  held  over  the  maximum  distance  if  neces- 
sary. 

Calls  should  not  be  prolonged  beyond  fifteen  seconds,  and  should  be  foilowed  by 


WIRELESS  COURSE— LESSON  NO.  15  119 

the  letters  of  the  station  calling.  If,  after  making  the  call,  a  ship  hears  the  signal 
"B  K"  or  "XXXX"  made,  she  should  take  it  to  mean  that  one  station  communicating 
with  another  is  being  interfered  with  by  her  calls,  and  that  she  should  wait. 

After  the  station  called  acknowledges  the  call,  the  vessel  should  report  her  posi- 
tion. The  following  manner  of  reporting  position,  etc.,  is  preferred: 

a.  Distance  of  the  vessel  from  the  coast  station  in  nautical  miles. 

b.  Her  true  bearing  from  coast  station  in  degrees,  counted  from  0  to  360. 

c.  Her  true  course  in  degrees,  counted  from  0  to  360. 

d.  Her  speed  in  nautical  miles  per  hour. 

e.  The  number  of  messages  she  desires  to  transmit. 

This  will  enable  the  coast  station  receiving  a  number  of  calls  from  various 
vessels,  to  determine  which  one  will  pass  out  of  range  first,  in  order  that  that  vessel 
may  be  permitted  to  finish  her  business.  When  a  coast  station  acknowledges,  she  may 
state  whether  or  not  she  has  messages  for  the  ship,  and  if  she  cannot  communicate 
further  with  the  ship  at  that  time,  the  ship  will  be  informed  of  the  length  of  the 
time  it  will  be  necessary  to  wait. 

On  receiving  word  to  "go  ahead"  the  vessel  should  send  a  message  as  follows: 

a.  "H  R"  or  "M  S  G." 

b.  Number  of  message. 

c.  Ship's  call  letters. 

d.  Operator's  sign. 

e.  Number  of  words,  excluding  address  and  signature. 

f.  Original  station  and  number,  for  relayed  messages  only. 

g.  Original  date,  for  relayed  messages  only. 
h.     Route  of  message. 

i.      Address. 

j.      Message  (body). 

k.     Signature. 

In  case  of  long  messages,  the  sending  ship  should  get  acknowledgment  after 
every  twenty  words  or  thereabouts,  before  proceeding. 

Communication  may  be  interrupted  at  any  time,  and  the  right  of  way  given 
to  a  Government  station  or  vessel,  if  necessary,  or  to  any  vessel  in  distress,  or  to 
send  broadcast  any  important  information. 

All  stations  may  be  expected  to  be  familiar  with  the  methods  of  communication 
adopted  by  the  International  Wireless  Conference  of  Berlin,  of  1906,  with  special 
regard  to  the  international  signal  of  distress,  "S  O  S,"  and  the  signal  "P  R  B," 
expressing  the  desire  to  communicate  by  means  of  the  international  signal  code  by 
wireless.  Ships  are  requested  not  to  use  the  letters  "O  S"  preceding  a  position  report, 
as  the  letters  "O  S"  made  rapidly  and  continuously  might  be  mistaken  for  the  signal 
of  distress,  "S  O  S." 

Shore  stations  in  designating  the  order  in  which  messages  will  be  received  from 
the  vessels  within  range,  will  be  guided  exclusively  by  the  necessity  of  permitting 
each  station  concerned  to  exchange  the  greatest  possible  number  of  wireless  tele- 
grams. At  all  times  business  may  be  expected  to  be  handled  in  the  following  order: 

a.  Government   business,  viz.,   telegrams   from   any   Government   Department   to 
its  agent  aboard  ship. 

b.  Business   concerning   the   vessel   with   which   communication   has   been   estab- 
lished, viz.,  telegrams  from  owner  to  master. 

t  c.     Urgent  private  dispatches,  limited. 

d.  Press  dispatches. 

e.  Other  dispatches. 


-APPENDIX- 


NAVIGATION  SERVICE  FORM  751. 
Operator's  Certificate  of  Skill  in  Radio-Communication. 

This  is  to  certify  that,  under  the  provisions  of  the  Act  of  June  24,  1910 

.'...,  has  been  examined  in  radio-communication  and  has  passed  in: 

a.  The    adjustment    of    apparatus,    correction    of    faults,    and    change    from    one 
wave-length   to  another; 

b.  Transmission  and  sound  reading  at  a  speed  of  not  less  than  fifteen  words  a 
minute,  American  Morse,  twelve  words  Continental,  five  letters  counting  as  one  word. 

The  candidate's  practical  knowledge  of  adjustment  was  tested  on  a  

set   of  apparatus.      His   knowledge   of   other   systems   and   of   international   radio-tele- 
graphic regulations  and  American  naval  wireless  regulations  is  shown  below: 

(Signature    of   examining   officer)    

Place ,  Date   ,  191 

By  direction  of  the   Secretary  of  Commerce  and  Labor. 


Commissioner   of   Navigation,   Washington,    D.    C. 

I. ,   do   solemnly   swear   that   I   will   faithfully  preserve   the 

secrecy  of  all  messages  coining  to  my  knowledge  through  my  employment  under  this 
certificate;  that  this  obligation  is  taken  freely,  without  mental  reservation  or  purpose 


120  WIRELESS  COURSE— LESSON  NO.  15 

of  evasion;  and  that  I  will  well  and  faithfully  discharge  the  duties  of  the  office:     So 
help  me  God. 

(Signature  of  holder) 

Date  of  birth,    ' 

Place   of  birth, 

Sworn  to  and  subscribed  before  me  this day  of A.  D.,  191.... 

(Seal)  , 

Notary   Public. 

The  certificate  as  issued  is  valid  for  a  period  of  two  years. 

The  following  is  an  excerpt  from  a  "Treatise  on  Wireless  Telegraphy,"  by  H. 
Gernsback,  regarding  the  New  Wireless  law  effective  since  Dec.  13,  1912,  affecting 
private  Radio  stations: 

THE  WIRELESS  ACT. 

"Be  it  enacted  by  the  Senate  and  House  of  Representatives  of  the  United  States 
of  America,  in  Congress  assembled;  That  a  person,  company,  or  corporation  within 
the  jurisdiction  of  the  United  States  shall  not  use  or  operate  any  apparatus  for  radio 
communication*  as  a  means  of  commercial  intercourse  among  the  several  States,  or 
with  foreign  nations,  or  upon  any  vessel  of  the  United  States  engaged  in  Interstate  or 
foreign  commerce,  or  for  the  transmission  of  radiograms  or  signals  the  effect  of  which 
extends  beyond  the  jurisdiction  of  the  State  or  Territory  in  which  the  same  are  made, 
or  where  interference  would  be  caused  thereby,  with  the  receipt  of  messages  or  sig- 
nals from  beyond  the  jurisdiction  of  the  said  State  or  Territory,  except  under  and  in 
accordance  with  a  license,  revocable  for  cause,  in  that  behalf  granted  by  the  Secretary 
of  Commerce  and  Labor  upon  application  therefor;  but  nothing  in  this  Act  shall  be 
construed  to  apply  to  the  transmission  and  exchange  of  radiograms  or  signals  between 
points  situated  in  the  same  State;  Provided,  That  the  effect  thereof  shall  not  extend 
beyond  the  jurisdiction  of  the  said  State  or  interfere  with  the  reception  of  radiograms 
or  signals  from  beyond  said  jurisdiction." 

*Wireless  Telegraph  or  Telephone  sending  stations  included. 

GENERAL  RESTRICTIONS  ON  PRIVATE  STATIONS. 

"Fifteenth.  No  private  or  commercial  station  not  engaged  in  the  transaction  of 
bona  fide  commercial  business  by  radio  communication  or  in  experimentation  in  con- 
nection with  the  development  and  manufacture  of  radio  apparatus  for  commercial 
purposes  shall  use  a  transmitting  wave  length  exceeding  two  hundred  meters  or  a 
transformer  input  exceeding  one  kilowatt  except  by  special  authority  of  the  Secretary 
of  Commerce  and  Labor  contained  in  the  license  of  the  station;  Provided,  That  the 
owner  or  operator  of  a  station  of  the  character  mentioned  in  this  regulation  shall  not 
be  liable  for  a  violation  of  the  requirements  of  the  third  or  fourth  regulations  to  the 
penalties  of  one  hundred  dollars  or  twenty-five  dollars,  respectively,  provided  in  this 
section  unless  the  person  maintaining  or  operating  such  station  shall  have  been  noti- 
fied in  writing  that  the  said  transmitter  has  been  found  upon  tests  conducted  by  the 
Government,  to  be  so  adjusted  as  to  violate  the  said  third  and  fourth  regulations, 
and  opportunity  has  been  given  to  said  owner  or  operator  to  adjust  said  transmitter 
in  conformity  with  said  regulations. 

SPECIAL   RESTRICTIONS   IN   THE   VICINITIES   OF   GOVERNMENT 

STATIONS. 

"Sixteenth.  No  station  of  the  character  mentioned  in  regulation  fifteenth  sit- 
uated within  five  nautical  miles  of  a  naval  or  military  station  shall  use  a  transmitting 
wave  length  exceeding  two  hundred  meters  or  a  transformer  input  exceeding  one- 
half  kilowatt." 

The  license  is  free,  it  costs  not  a  penny.  All  that  is  required  of  you  is  that  you 
are  familiar  with  the  law  and  that  you  can  transmit  messages  at  a  fair  degree  of  speed. 
The  law  does  not  require  that  you  take  an  examination  in  person  if  you  are  located 
too  far  from  the  nearest  radio  inspector. '  All  you  have  to  do  is  to  take  an  oath  before 
a  notary  public  that  you  are  conversant  with  the  law  and  that  you  can  transmit  a 
wifeless  message.  If  you  wish  to  be  licensed — and  we  urge  all  amateurs  to  do  so,  as 
it  is  a  great  honor  to  own  a  license — write  your  nearest  Radio  Inspector  (see  below), 
and  be  will  forward  the  necessary  papers  to  you  to  be  signed. 

R?dio  inspectors  are  located  at  the  following  points:  (Address  him  at  the  Cus- 
toms House): 

Boston,  Mass.,  New  York,  N.  Y.,  Baltimore,  Md.,  Savannah,  Ga.,  New  Orleans;  La.; 
San  Francisco,  Cal.,  Seattle,  Wash.,  Cleveland,  Ohio,  and  Chicago,  111.  Also  the  Com- 
missioner of  Navigation,  Department  of  Commerce  end  Labor,  Washington,  D.  C. 

SECRECY  OF  MESSAGES. 

"Nineteenth.  No  person  or  persons  engaged  in  or  having  knowledge  of  the  op- 
eration of  any  station  or  stations,  shall  divulge  or  publish  the  contents  of  any  mes- 
sages transmitted  or  received  by  such  station,  except  to  the  person  or  persons  to  whom 
the  same  may  be  directed,  or  their  authorized  agent,  or  to  another  station  employed 
to  forward  such  message  to  its  destination,  unless  legally  required  to  do  so  bv  the 
court  of  competent  jurisdiction  or  other  competent  authority.  Any  person  guilty  of 
divulging  or  publishing  any  message,  except  as  herein  provided,  shall,  on  conviction 
thereof,  be  punishable  by  a  fine  of  not  more  thgn  two  hundred  and  fifty  dollars  or 
imprisonment  for  a  period  of  not  cx^^eding  three  months,  or  both  fine  and  impris- 
onment in  the  discretion  of  the  court." 


WIRELESS    COURSE— LESSON   NO.    16 


121 


Lesson  Number  Sixteen. 


COMMERCIAL  SHIP  AND  LAND  WIRELESS  STATIONS. 

•HEN  wireless  telegraphy  was  first  developed  into  a  commercial  possibility,  by 
Marconi,  a  few  years  ago,  the  principal  long  distance  tests  were  carried  on 
from  land  stations,  and  so  it  is  logical  to  open  this  paper  with  a  description 
of  the  various  characteristics  connected  with  them,  in  contradistinction  to  the  floating 
stations  on  board  ship. 

To  begin  with,  radio-telegraphic  stations  on  land  always  have  the  decided  advan- 
tage over  ship  stations,  in  that  they  have  unlimited  space  over  which  to  spread  their 
aerial  wire  systems,  which  are  quite  frequently  of  massive-  proportions,  as  for  instance 
the  one  erected  at  the  Marconi  Trans-Atlantic  station,  located  at  Glace  Bay,  Nova 
Scotia. 

This  aerial  is  built  in  the  form  of  a  huge  inverted  pyramid,  about  400  feet  in  height, 
and  250  feet  long  on  each  of  its  four  sides. 

The  transmitting  apparatus  consists  of  suitable  step-up  high  voltage  transformers 
and  an  alternating  current  generator  of  150  kilowatts  capacity.  The  sending  apparatus 
includes  all  the  necessary  condensers,  oscillation  transformers,  etc.  The  discharging 
apparatus  is  mounted  in  a  special  and  separate  room.  The  operators  have  to  use 
cotton  in  their  ears  while  sending,  owing  to  the  terrible  crash  of  the  spark,  which  is 
audible  for  several  miles.  The  sending  operator  sits  in  a  chair  mounted  upon  a 
glass  platform,  to  prevent  getting  severely  shocked,  while  he  handles  the  key  which 
puts  the  "thunder  factory"  into  life,  this  being  the  term  .once  conferred  upon  it, 
owing  to  the  enormous  noise  and  pyrotechnical  display  occurring  when  this  mas'todon 
of  wireless  plants  gets  into  operation. 

A  lofty  wire  fence  surrounds  the  entire  plant  and  aerial,  so  that  no  one  can 
accidentally  get  near  enough  to  the  highly  charged  portions  to  get  shocked,  and 
probably  killed.  The  aerial  emits  a  large  brush  discharge,  which  is  very  pretty 
to  watch  at  night,  and  resembles  a  million  golden  threads  reaching  out  into  the 
darkness. 


(Courtesy  "Modern   Electrics.") 


Fig.  1 


A  view  of  the  condenser  room  of  one  of  -the  highest  powered  wireless  stations 
in  Europe,  that  situated  at  Nauen,  Germany,  is  illustrated  by  fig.  1.  The  capacity  of 
the  transmitting  plant  is  25  kilowatts,  with  50  "cycle  alternating  current,  used  to  sup- 
ply the  large  step-up  transformers. 

Copyright  1912  by  E.   I.   Co. 


122 


WIRELESS   COURSE— LESSON   NO.   16 


A  special  transmitting  relay  for  controlling  the  extremely  heavy  primary  current 
is  always  used  in  these  large  stations.  Instead  of  opening  the  primary  circuit  of 
the  transformers  at  the  Nauen  station,  the  transformer  primary  coils  are  short- 
circuited  to  discharge  the  condenser  jars,  of  which  there  are  360.  To  again  charge 
the  jars,  the  "short''  across  the  primary  winding  of  the  transformer  is  opened  by 
means  of  the  relay.  This  scheme  was  found  expeditious  to  the  best  handling  of  the 
extra  heavy  currents  involved. 

The  lofty  aerial  structure,  of  steel  lattice-work  and  resting  on  a  base  pillar  of 
glass,  is  arranged  so  that  the  insulated  metal  tower  can  be  employed  as  a  part  of  the 
aerial  system,  the  aerial  wires  being  spread  out  to  form  a  large  umbrella,  with  a 
total  spread  of  about  70,000  square  yards.  The  height  of  the  aerial  mast  or  -tower 
is  330  feet.  The  steel  guys,  steadying  the  tower,  are  well  insulated  at  frequent 
intervals. 

The  aerial  and  its  tower  are  depicted  in  fig.  2.  The  charging  current  applied  to 
the  aerial  and  ground  represents  a  spark  over  3  feet  in  length  and  very  fat. 

It  is  interesting  to  note  the  way  in  which  the  ground  for  such  a  large  station 
as  this  is  made.  Water  was  found  but  six  feet  below  the  surface  of  the  earth,  which 
assured  a  damp  earth  connection.  The  ground  was  composed  of  a  set  of  spreading 
iron  wires,  to  the  number  of  108,  radiating  under  ground  in  all  directions,  and  these 
were  further  augmented  by  branching  off  at  certain  distances,  so  as  to  make  a  grand 
total  of  324  wires  for  the  earth.  The  total  area  covered  by  the  ground  wires  amounted 
to  approximately  150,000  square  yards,  or  considerably  more  than  that  covered  by 
the  aerial.  From  the  centre  of  the  radiating  ground  wires,  one  heavy  main  cable 
leads  into  the  station. 


Fig.  2  (Courtesy  "Modern  Electrics.") 

A  view  of  the  aerial  and  also  the  operating  room  of  the  United  Wireless  Com- 
pany's station  at  No.  42  Broadway,  New  York  City,*  is  illustrated  by  the  cuts  figs. 
3  and  4.  The  transmitting  set  shown  here  is  of  2  kilowatts  capacity,  but  has  been 
increased  to  5  K.  W.  at  the  present  time.  A  loose-coupled  oscillation  transformer 
is  also  used  now,  instead  of  a  helix.  The  spark  gap  is  a  special  one,  of  the  ventilated 
muffled  type. 

In  small  size  land  stations,  the  ground  connection  where  convenient  and  per- 
missable  is  made  to  the  water  pipe,  or  main.  Where  this  is  impracticable,  the  ground 
must  be  made  separately,  either  by  sinking  a  standard  type  of  ground  plate,  such 
as  the  Lord  Electric  Company's  design,  in  moist  earth,  or  a  net-work  of  radiating 
wires  may  be  buried  in  damp  earth,  or  placed  just  above  it,  this  acting  as  a  counter- 
poise, and  is  much  employed  in  military  portable  sets  used  by  the  U.  S.  Signal  Corps. 

The  main  ground  lead  must  not  be  smaller  than  No.  4  B.  &  S.  gauge  copper 
wire,  or  the  equivalent  in  conductivity,  and  preferably  of  stranded  form,  this  size 
of  conductor  being  required  by  the  Fire  Underwriters  Rules.  The  branch  wires, 
where  a  counterpoise  ground  net  is  used,  can  be  of  a  smaller  size  than  the  main 
ground  wire,  as  these  will  be  called  upon  to  carry  only  a  part  of  the  total  radiation 
current. 

In  all  stations,  the  wiring  of  the  primary  circuits  must  conform  to  the  Under- 

*Now  owned  by  The  Marconi  Wireless  Telegraph  Co. 


WIRELESS   COURSE— LESSON   NO.   16 


123 


writers   Rules,   and   the   aerial    system   is   required   to   be   provided   with    satisfactory 
grounding  switches  to  serve  in  case  of  storms  of  the  electrical  variety. 

Land    wireless  stations,    i.  e.,    stationary  ones,    usually  derive    their  transformer 
current    from    a    motor-generator    set,    the    motor    taking    its    quota    of    current    from 


(Courtesy  "Modern  Electrics.") 


Fis 


(Courtesy  "Modern   Electrics.")  Fig.  4 

the  building  mains,  or  wires,  and  the  generator  it  drives,  supplying  an  alternating 
current  with  a  frequency  of  from  60  to  500  cycles  per  second.  The  higher  frequency 
is  being  extensively  adopted  all  over  now,  as  it  makes  possible  a  very  high  spark 


•'* 


124 


WIRELESS   COURSE— LESSON    NO.    16 


frequency,  which  carries  a  great  deal  further  than  the  ordinary  low  frequency  spark, 
which  is  particularly  good  for  penetrating  through  bad  static  or  interference. 

Where  stations  are  isolated,  or  do  not  have  available  the  necessary  current  to  drive 
a  motor,  a  gasoline  or  kerosene  oil  engine  is  pressed  into  service,  and  made  to  drive 
an  alternating  current  dynamo,  steam  engines  also  being  used. 

In  the  important  land  stations,  operators  are  on  duty  all  the  time,  each  operator 
doing  a  turn  of  from  8  to  10  hours  generally. 

The  shore  and  inland  stations  maintained  by  the  Marconi  Wireless  Telegraph 
Company,  which  is  the  principal  commercial  company  operating  at  this  time,  vary  in 
size  from  2  to  10  kilowatts,  sending  capacity,  although  there  are  a  few  installations 
at  certain  important  points,  with  a  sending  power  of  25  kilowatts. 

The  sending  speed  in  most  of  these  stations  often  reaches  forty  or  more  words 
per  minute,  under  good  conditions. 

In  changing  from  transmitting  to  receiving  instruments,  a  number  of  the  stations 
have  abolished  the  aerial  switcjh,  which  is  usually  large  and  clumsy  to  manipulate, 
especially  when  a  large  number  of  messages  are  to  be  sent  and  received.  The  system 
known  as  the  "break-key"  change  over,  is  much  in  use  for  this  purpose,  being  very 
quick  and  efficient  if  properly  applied  to  the  particular  apparatus  of  which  it  is 
made  a  part  of. 


Fig.  5 


In  diagram  fig.  5,  is  illustrated  the  connections  of  a  simple  break-key  circuit. 
As  can  be  readily  seen,  the  key,  when  closed  to  excite  the  transmitting  apparatus, 
also  closes  an  auxiliary  contact  through  a  relay  and  battery  shown.  The  relay 
operates  to  cut-out  the  receiving  instruments  by  short-circuiting  them,  and  it  has 
been  necessary  in  most  cases  to  also  arrange  the  relay  to  short-circuit  the  detector, 
or  it  becomes  disturbed  in  its  adjustment,  whenever  the  sending  instruments  are 
excited. 


'  (Courtesy  "Modern   Electrics.") 


Fig.  6 


In  the  break-key  system  here  described,  the  operator  listens-in  and  receives 
through  the  transmitting  helix,  but  this  makes  practically  no  difference,  as  it  has 
a  low  inductance  value. 

Having  reviewed  the  salient  features  of  the  land  wireless  stations,  attention  can 
now  be  turned  to  those  aboard  a  ship,  and  here  things  are  a. little  different  in  some 
ways,  due  to  natural  conditions  obtaining  in  consequence  of  limited  space,  and  other 
peculiarities. 

Probably  the  most  noticeable  difference  between  land  and  ship  stations,  is  in  the 
layout  of  the  aerial.  Only  a  limited  space  is  allowable  for  this  part  of  the  wireless 


WIRELESS  COURSE— LESSON  NO.  16 


125 


equipment,  and  the  best  possible  design  of  aerial  for  a  certain  height  and  length 
must  be  put  up. 

Ship  aerials  are  generally  of  the  inverted  L,  or  T  type  either  straight-away  or 
looped,  according  to  the  instruments  employed.  Stranded  phosphor  bronze  cable  is 
most  always  utilized,  the  number  of  spans  varying  from  two  to  six  or  more;  depend- 
ing upon  the  size  of  the  ship  and  the  wireless  set. 

The  aerial  is  stretched  between  the  mast-heads,  on  the  majority  of  vessels,  some- 
what after  the  fashion  depicted  at  fig.  6,  the  lead-in  wires  from  it,  coming  down  to 
the  wireless  cabin  in  as  straight  a  line  as  possible. 


Fig.  7  Fig.  7a 

(Courtesy  "Modern   Electrics.") 

The  ground  for  the  wireless  set  on  ship  board  is  of  course  ready  at  hand 
in  the  steel  hull  of  most  vessels,  and  the  ground  wire  is  soldered  or  otherwise 
secured  to  a  brass  plug,  threaded  into  a  hole  in  the  steel  framework,  as  near  the 
water  plates  as  possible.  This  must  be  done  for  the  reason  that  sometimes,  a  very 
good  electrical  connection  is  not  present  between  the  joints  in  the  steel  work,  owing 
to  the  red  lead  upon  and  between  the  surface. 


Fig  8 


(Courtesy  "Modern  Electrics.") 


On  wooden  vessels,  the  ground  connection  has  to  be  taken  care  of  in  another 
way,  but  may  in  some  cases  be  secured  to  the  copper  bottom,  which  covers  most 
wooden  hulls.  The  ground  lead  wire  is  run  up  the  side  of  the  ship  in  this  case,  in 
as  short  a  line  as  possible  to  the  instruments. 

Failing  this  facility  for  establishing  a  ground,  it  becomes  necessary  to  improvise 
one,  by  securing  a  metal  plate,  preferably  of  copper,  to  the  outside  of  the  hull,  and 
below  the  water  line.  From  this  a  wire  is  run  over  the  side  of  the  vessel  on  insulators, 
to  the  instruments.  A  plate  of  1-16  inch  thick  copper,  about  3  by  10  feet,  forms  a 
very  good  ground  for  stations  up  to  \l/2  kilowatts  capacity. 

A  glimpse  of  the  operating  room  on  a  ship,  is  given  by  the  cuts,  figs.  7  and  7a,  which 


126 


WIRELESS  COURSE— LESSON  NO.  16 


depicts  an  equipment  supplied  for  special  service  during  the  Hudson-Fulton  Celebra- 
tion, at  New  York  City,  by  the  Electro  Importing  Company,  also  of  New  York. 
The  aerial  leads  can  be  seen  entering  the  wireless  room,  through  the  side  cf  the  cabin. 
This  set  was  rated  at  J/2  K.  W.  and  the  transformer  coil,  operated  from  110  volts 
D.  C.  through  the  medium  of  a  Gernsback  electrolytic  interrupter. 

In  fig.  8,  is  shown  the  arrangement  of  the  apparatus  in  a  5  K.  W.  set  on  the 
Steamship  "Korea,"  which  broke  a  world's  record  for  its  size,  by  transmitting  4,700 
miles  at  night  and  675  miles  in  broad  daylight,  with  sun  shining. 

On  board  ship,  the  operator  usually  has  his  bunk  in  the  wireless  room,  excepting 
on  large  vessels  and  men-o-war,  where  more  than  one  operator  is  on  the  staff,  in 
which  event  separate  sleeping  and  living  quarters  are  provided.  An  operator  on  a 
commercial  ship  is  obliged  to  sign  the  ship's  articles  or  papers  and  is  qualified  as  a 
non-commissioned  officer,  being  under  the  direct  supervision  of  the  captain  in  com- 
mand. 


Fig.  9 


(Courtesy  "Modern  Electrics.") 


The  salary  of  ship  operators  varies  from  50  to  75  dollars  per  month,  with  meals 
and  berth  free,  also  medical  attendance  when  required.  The  life  of  a  wireless  operator 
at  sea  is  an  interesting,  congenial  and  broadening  one,  serving  to  educate  a  man 
as  no  other  one  thing,  for  there  is  no  better  educator  than  travel. 

Returning  to  the  ship's  wireless  apparatus  again,  it  may  be  said  that,  at  present 
the  usual  equipment  comprises  a  2  to  5  kilowatt  set,  made  up  of  a  motor-generator, 
for  the  transmitting  current  source,  the  motor  deriving  its  current  from  the  ship's 
electric  plant  in  the  main  engine  room.  The  motor  drives  an  alternating  current 
generator,  which  supplies  A.  C.  at  110  volts  or  more  pressure,  with  a  frequency  of  60 
or  more  cycles  per  second.  The  sending  transformer  is  of  either  the  open  or  closed 
core  type,  the  open  core  predominating. 

The  primary  transformer  current  is  generally  broken  up  into  dots  and  dashes, 
by  means  of  an  ordinary  Morse  key  of  extra  heavy  construction,  but  some  sets  are 
equipped  with  an  oil  break-key,  or  a  relay  operated  by  a  common  key. 

On  commercial  vessels,  the  wireless  room  is  frequently  located  on  one  of  the 
tipper  decks,  which  facilitates  the  leading  in  of  the  aerial  wares  to  the  instruments, 
and  also  keeps  the  cabin  more  free  from  being  flooded  in  times  of  storm  or  a  heavy 
sea.  A  speaking  tube  or  telephone  connects  the  wireless  cabin  with  the  captain's 
cabin,  pilot-house,  and  other  vital  parts  of  the  ship. 

On  battleships  the  wireless  room  is  in  virtue  of  its  extreme  importance,  placed 
in  as  safe  and  invulnerable  a  part  of  the  ship  as  possible.  On  the  U.  S.  Battleship 
Iowa,  it  is  located  just  back  of  the  rear  gun  turret,  in  a  well  armored  cabin.  The 
aerial  is  supported  from  the  new  style  shot-proof  skeleton  mast,  ensuring  the  opera- 
tion of  the  station  as  long  as  the  vessel  floats  practically,  unless  a  chance  shot  hap- 
pened to  hit  the  aerial  supporting  cables. 

The  Bellin-Tosi  system,  employing  a  special  directive  form  of  aerial,  which  makes 
it  possible  to  concentrate  the  direction  of  the  waves  radiated,  was  applied  to  a  com- 
mercial ship,  with  considerable  success.  A  cut  of  the  aerial,  which  is  of  triangular 
form,  on  the  steamship  "La  Provence,"  is  shown  at  fig.  9.  It  is  supported  from  a 


WIRELESS  COURSE— LESSON  NO.  16 


127 


wire  cable  strung  between  the  masts.  This  system  of  a  directive  aerial  is  thoroughly 
discussed  in  the  lesson  on  aerials. 

The  apparatus  in  ship  stations,  is  made  as  simple  and  strong  as  possible,  as  it 
is  not  an  easy  matter  to  get  or  to  fit  new  parts,  when  the  vessel  is  on  the  high 
seas.  Duplicate  parts  of  such  instruments  as  glass  condenser  jars,  detector  supplies 
and  one  or  two  spare  detectors,  a  spare  set  of  head  receivers,  an  extra  sending  key, 
and  other  things,  are  or  should  be  carried  at  all  times. 

Most  of  the  commercial  ship  stations  employ  an  oscillation  transformer,  for  tuning 
the  aerial  circuit.  The  condensers  are  of  the  glass  jar  or  tube  type,  with  their  metallic 
coatings  plated  securely  onto  the  glass,  to  reduce  blistering  to  a  minimum. 

The  transformers  or  induction  coils  for  ship  sets  are  invariably  impregnated  in 
a  solid  insulation,  such  as  wax,  as  oil  immersed  types  would  cause  more  or  less 
trouble  by  the  oil  leaking  out.  However,  in  some  larger  sets,  having  extra  high 
secondary  voltages,  the  transformer  windings  are  immersed  in  oil. 


Fig.  10 


The  receiver  sets  for  this  class  of  service  comprise  a  loose-coupler  or  receiving 
transformer,  variable  condensers,  Pyron  or  Perikon  detectors,  and  sometimes  a  Flem- 
ing valve  or  Marconi  Hysteresis  cymoscope.  The  head  telephones,  for  the  Perikon 
or  other  crystal  rectifying  detectors,  is  of  good  make  and  of  not  greater  resistance 
than  3,200  ohms.  Low  resistance  phones  (80  ohms  each)  are  used  with  the  Marconi 
Hysteresis  detector. 


Fig.  11 

The  following  is  a  copy  of  the  United  States  law  regarding  the  compulsory  wire- 
less equipment  of  sea-going  vessels. 

"Be  it  enacted  by  the  Senate  and  House  of  Representatives  of  the  United  States 
of  America  in  Congress  assembled:  That  from  and  after  the  first  day  of  July, 
nineteen  hundred  and  eleven,  it  shall  be  unlawful  for  any  ocean-going  steamer  of 
the  United  States,  or  of  any  foreign  country,  carrying  passengers,  or  fifty  or  more 
persons,  including  passengers  and  crew,  to  leave  or  attempt  to  leave  any  port  of  the 
United  States,  unless  such  steamer  shall  be  equipped  with  an  efficient  apparatus  for 
radio-communication,  in  good  working  order,  in  charge  of  a  person  skilled  in  the 
use  of  such  apparatus;  which  apparatus  shall  be  capable  of  transmitting  and  receiving 


128 


WIRELESS  COURSE— LESSON  NO.  16 


messages  over  a  djstanc?  of  at  least  one  hundred  miles,  night  or  day:  Provided, 
That  the  provisions  of  this  Act  shall  not  apply  to  steamers  plying  only  between  ports 
less  than  two  hundred  miles  apart." 


Fig.  12 


(Courtesy  "Modern  Electrics.") 


In  cuts  No.  10  and  11  are  shown  two  typical  aerials  for  ships.     At  fig.  12  is  illus- 
trated a  Portable  Pack  Set  carried  by  a  Mule. 


Fig.  13 
A  Telefunken  portable  wagon  set,  for  army  purposes  is  seen  at  fig.  13. 


WIRELESS  COURSE— LESSON  NO.  17 


129 


Lesson  Number  Seventeen. 


HIGH  FREQUENCY  CURRENTS. 

A  HIGH  frequency  current  is  generally  understood  to  mean  an  oscillating  or  alter- 
nating current,  whose  speed  or  frequency  of  reversal  in  direction  occurs  at  a 
much  higher  rate  than  that  obtaining  in  commercial  lighting  circuits,  where  the 
frequency  does  not  exceed  120  cycles  or  240  alternations  per  second. 

It  will  be  easier  to  understand  just  what  is  meant  here  probably,  in  speaking: 
of  high  frequency  currents,  by  glancing  at  the  curves  shown  in  fig.  1.  In  the  curve 
representing  a  60  cycle  alternating  current  at  A,  is  seen  that  each  alternation 
requires  one-half  of  1-60  second  or  1-120  second,  to  take  place  in:  two  alternations 


1- ALTERNATION  OR 
1/2 -CYCLE. 

4- MAX.  CURRENT. 


A 


0 


MAX- 


TIME. 


0-  CURRENT. 


<-/60  SECOND  -J 


B 


MAX.  CURRENT. 


<-l/60  SECOND ->| 


TIME 


—  MAX.  CURRENT 


Fig.  1 


0- CURRENT 


making  a  complete  cycle  and  requiring  1-60  of  a  second,  or  there  will  be  60  cycles 
per  second,  or  also  3,600  per  minute,  which  is  that  commonly  used  for  electric  light 
and  motor  circuits. 

Looking  now  at  the  curve  B,  it  is  evident  that  where  formerly,  as  at  curve 
A,  only  one  cycle  of  the  current  occurred  in  each  1-60  of  a  second,  there  is  now  seven 
times  that  number  occurring  in  the  same  space  of  time,  or  the  frequency  in  cycles 
per  second  would  be,  7  times  60  or  420  cycles  per  second. 


Copyright  1912  by  K.   I.   Co. 


130  WIRELESS  COURSE— LESSON  NO.  17 

In  the  usually  accepted  meaning  of  the  term,  high  frequency,  however,  the 
number  of  cycles  occurring  per  second  is  not  any  such  low  figure  as  that  just  men- 
tioned, but  in  the  order  of  100,000  to  1,000,000  cycles  per  second. 

When  such  high  frequency  currents  as  these  are  employed,  many  wonderful  and 
unlocked  for  phenomena  take  place;  among  other  things,  the  currents  of  such  a 
frequency  can  be  handled  with  impunity,  and  even  passed  through  the  body,  not- 
withstanding that  the  voltage  may  be  several  million,  and  the  amperage  several 
amperes  (l/z  ampere  through  the  body  at  2,000  volts  D.  C,  or  low  frequency,  A.  C, 
means  death). 

High  frequency  currents  of  this  order  no  longer  obey  the  rules  governing  the 
ordinary  low  frequency  oscillating  currents.  For  one  thing,  they  travel  only  on  the 
surface  of  conductors,  not  through  them,  penetrating  only  a  few  thousandths  of  an 
inch  below  the  'surface,  this  phenomena  being  known  in  electrical  parlance  as  the 
"skin  effect,"  which  accounts  for  the  reason  that  these  currents  do  not  hurt  the 
body  when  handled,  i.  e.,  they  possibly  do  not  reach  far  enough  below  the  skin  of  the 
body,  to  shock  or  destroy  the  nerves  and  muscles.  This  is  the  theory  in  general 
acceptance  to-day. 

A  great  part  of  our  knowledge  of  these  high  frequency  currents  is  due  to  the 
untiring  and  exhaustive  researches  of  Nikola  Tesla,  a  well  known  Electrical  Engineer 
and  Scientist,  after  whom  the  Tesla  coil,  which  .is  used  to  produce  high  frequency 
currents  with,  is  named.  To  the  student  interested  in  this  little  known  field  of  elec- 
trical science,  it  is  recommended  that  he  procure  a  copy  of  Mr.  Tesla's  book,  "Experi- 
ments with  Currents  of  High  Potential  and  High  Frequency." 

High  frequency  alternating  currents  may  be  produced  by  a  special  dynamo, 
such  as  Prof.  Fessenden's,  or  by  a  regular  high  frequency  disruptive  discharge  set, 
employing  a  step-up  transformer  excited  by  another  high  voltage  transformer  or 
induction  coil,  coupled  with  a  spark  gap  and  condenser  in  the  exciting  circuit,  after 
the  manner  depicted  in  fig.  2,  which  is  the  commonest  arrangement. 

In  the  diagram  shown,  I  is  the  induction  coil  of  not  less  than  2  inch  spark 
capacity.  T  is  the  air  core,  Tesla  or  high  frequency  transformer,  serving  to  step-up 
the  voltage  delivered  by  the  induction  coil  secondary  to  many  times  its  original 
value.  C  is  a  condenser  composed  of  glass  plates,  coated  with  tin  foil  on  both  sides, 
or  regular  leyden  jars.  S  G  is  the  spark  gap,  in  which  the  disruptive  discharge  of  the 
condenser  takes  place.  G  is  the  discharge  gap  of  the  Tesla  coil  secondary  winding, 
across  which  the  high  frequency  oscillations  surge. 


(Courtesy  "Modern  Electrics.")  Fig.  2 


The  action  of  the  apparatus  is  as  follows: — The  induction  coil  or  transformer 
I,  is  excited  from  the  battery  shown  at  B  or  the  regular  line  wires,  and  its  secondary 
current  at  10,000  volts  pressure  or  more,  is  caused  to  charge  the  condenser  C,  which 
immediately  discharges  itself  through  the  primary  coil  of  the  Tesla  transformer  P, 
and  the  spark  gap  S  G;  and  due  to  the  conditions  imposed  by  such  a  circuit,  the 
condenser  discharge  becomes  not  a  single  oscillation  for  each  cycle  of  induction 
coil  current,  but  many  thousand,  so  that  with  certain  proportions  to  the  circuits 
as  regards  their  inductance  and  capacity,  the  frequency  of  the  current  passing  through 
the  Tesla  coil  primary,  may  reach  a  million  or  more  cycles  per  second,  rendering 
the  current  harmless  owing  to  the  "skin  effect"  already  mentioned.  The  currents 
thus  produced  are  of  course  highly  damped;  i.  e.,  the  series  of  oscillations  corre- 
sponding to  each  cycle  of  primary  transformer  current,  dies  down  to  zero  before  the 
next  series  of  oscillations  start. 

Tesla,  in  his  early  experiments  employed  a  high  potential  transformer  of  small 
dimensions  immersed  in  boiled-out  linseed  oil,  to  keep  it  from  breaking  down,  as  the 
strain  between  separate  turns  and  individual  windings  is  enormous.  However,  most 
of  the  large  high  frequency  sets  built  to-day,  utilize  a  Tesla  coil  with  air  insulation, 
taking  care  to  sufficiently  space  the  different  turns  and  windings,  so  that  they  cannot 
break  down.  There  is,  however,  a  considerable  loss  in  efficiency  incurred  by  using 


WIRELESS  COURSE— LESSON  NO.  17 


131 


these  coils,  as  the  permeability  of  the  air  for  magnetic  induction  is  very  inferior, 
and  the  greater  the  distance  separating  the  windings  of  such  a  coil,  the  lower  the 
efficiency,  as  the  air  gap  to  be  bridged  by  electro-magnetic  lines  of  force  is  also 
longer.  Hence,  if  this  space  between  windings  can  be  kept  down  to  a  low  figure,  the 
resultant  activity  of  the  secondary  coil  of  the  Tesla  transformer  will  be  vastly  greater, 
and  so  the  oil  immersed  coil  originally  used  by  Tesla  was  the  most  powerful  and 
efficient  for  a  giveji  consumption  of  watts. 

The  most  efficient  Tesla  coil,  is  then,  for  a  certain  size,  made  by  keeping  the 
primary  and  secondary  windings  as  close  together  as  possible,  which  is  best  done 
by  covering  the  secondary  winding,  usually  the  inner  one,  with  a  stout  insulating 
tube  of  hard  rubber,  glass  or  mica,  having  a  fairly  thick  wall  and  over-lapping  the 
ends  of  the  secondary  coil  a  short  distance.  The  primary  coil  can  be  wound  on  the 
outside  of  this  insulating  tube,  keeping  its  turns  pretty  well  in  the  centre  of  the 
tube,  and  several  inches  from  the  ends.  Then  the  whole  transformer  should  be 
immersed  in  an  oiltight  wooden  case  and  filled  with  transformer  oil  or  double-boiled 
linseed  oil.* 

All  tuned  wireless  transmitting  sets,  develop  high  frequency  oscillations  of 
great  periodicity.  This  will  be  apparent  upon  examination  of  the  diagram  fig.  3, 
which  shows  a  close-coupled  sending  set,  having  an  inductance  H,  a  condenser  C, 
a  spark  gap  S  P,  and  an  exciting  source  in  the  wireless  transformer. 


u 


(Courtesy  "Modern  Electrics.") 


Fig.  3 


In  this  case,  the  stepping  up  of  the  voltage  by  means  of  the  helix  is  accom- 
plished by  making  the  one  coil  serve  as  a  primary  coil,  charged  by  the  oscillatory 
or  condenser  circuit,  including  the  spark  gap;  and  also  as  a  secondary  coil  simul- 
taneously, to  charge  the  aerial  wire  and  ground.  If  the  aerial-ground  oscillating 
circuit  is  connected  to  embrace  more  turns  of  the  helix  inductance  than  the  closed  or 
condenser  oscillating  circuit,  then  the  voltage  impressed  upon  the  aerial  and  ground 
is  greater  than  that  in  the  closed  circuit,  by  that  ratio  representing  the  difference 
in  the  number  of  turns  in  each  circuit.  It  should  be  remembered  that  the  helix 
or  loose-coupler,  if  it  be  one,  does  not  change  the  frequency  of  the  current  in  itself, 
but  only  voltage  or  potential.  When  the  amount  of  turns  included  in  the  condenser 
or  closed  circuit  is  varied,  of  course,  the  frequency  will  then  also  vary,  as  it  depends 
upon  the  value  of  the  condenser  capacity  and  helix  inductance  in  circuit. 

It  is  possible  to  compute  the  frequency  of  the  osceillations  in  a  Tesla  coil  circuit, 
or  tuned  wireless  sending  circuit,  without  going  into  higher  mathematics.  To  begin 
with,  what  is  called  the  "oscillation  constant,"  is  first  determined,  being  the  square 
root  of  the  product  of  the  helix  inductance  in  centimeters,  and  the  condenser  capacity 
in  micro-farads.  Expressed  in  algebraic  form  it  is: — 


O  =  I'  C  XL; 

To  ascertain    the  inductance   in    centimeters   of  ithat    part   of  the    helix  included 
in  the  condenser  circuit,  the  following  formula  may  be  applied: — 

L  =  1  (TT  D  N)  2 


•For  particulars  on   the  construction   of  Tesla  coils,  etc..  see  "Construction   of  Induction  Coils 
and  Tr.-insforniors"  by  H.  \V.  Secor,  The  Electro  Supply  Co.,  N.'Y.  City.     25  Cents. 


132 


WIRELESS  COURSE— LESSON  NO.  17 


Where: — L  is  the  inductance  in  centimeters. 

is  3.1416  or  pi. 

D  is  the  diameter  of  the  helix  in  centimeters. 
N  is  the  number  of  turns  per  centimeter  of  helix  length. 
I  is  length  of  helix  in  centimeters. 

The  condenser  capacity  in  micro-farads,  or  C,  is  found  from  tests,  or  by  a  standard 
formula  as  given  in  the  lesson  on  "Mathematics  of  Wireless  Telegraphy." 


Fig.  4 


Fig.  5 


(Courtesy    "Modern     Electrics.") 


When  the  oscillation  constant  has  been  determined,  the  frequency  can  be  derived 
from  the  equation  below: — 


F  = 


5,033.000 
L  X  C 


WIRELESS  COURSE— LESSON  NO.  17 


133 


Where,    F  represents    the   frequency    in   cycles    per   second,    and 
is  the  oscillation  constant. 


c, 


The  frequency  in  wireless  stations  varies  from  a  hundred  thousand  or  less  up 
to  a  million  and  more  per  second,  depending  upon  the  wave-length  employed. 

A  very  neat  and  efficient  Tesla  transformer  designed  especially  for  experimental 
research,  is  built  by  the  Electro  Importing  Company^  of  New  York  City. 

A  cut  showing  their  instrument  in  full  activity  is  portrayed  at  fig.  4,  which  shows 
the  wonderful  display  it  gives  when  excited  from  a  two  inch  spark  coil  run  on  batteries. 
A  larger  exciting  spark  coil,  will  of  course  increase  the  activity  of  the  Tesla  coil 
considerably.  The  same  company  also  build  large  size  Tesla  transformers,  com- 
plete with  condensers,  rotary  spark  gaps,  and  exciting  transformers,  upon  request, 
from  six  ito  thirty-six  inch  Tesla  spark.  In  fig.  5,  is  shown  the  wiring  connections 
from  the  Tesla  transformer  mentioned  above.  The  transformer  itself  sells  for  an 
extremely  low  price  and  should  certainly  commend  itself  to  experimenters,  school 
laboratories,  and  demonstrators. 

Some  of  the  marvelous  and  mysterious  experiments  that  can  be  performed  with 
this  Tesla  coil  are  reproduced  in  the  cuts  figs.  5  and  6.  These  experiments  and 
numerous  others,  together  with  the  manner  of  making  them  are  fully  explained  in 
a  brochure  supplied  with  the  Tesla  coil. 

This  size  of  high  frequency  coil,  which  is  capable  of  delivering  three  to  four 
inch  sparks  at  its  secondary  terminals  when  excited  by  a  two  inch  spark  coil,  employs 
a  simple  fixed  spark  gap,  fitted  with  ball  or  pointed  electrodes,  flat  faced  one  having 
not  been  found  suitable  in  the  small  sets.  This  Tesla  high  frequency  set,  will  produce 
an  oscillatory  high  potential  current  of  several  hundred  thousand  volts,  at  a  periodicity 
of  half  a  million  cycles  per  second  or  more. 

In  large  high  frequency  outfits,  there  are  several  parts  of  the  apparatus  which 
require  a  little  change  in  design,  as  compared  with  the  set  previously  described,  owing 
to  the  heavier  currents  involved. 


TRANSFORMS*?' 


SPARK  GAP 

jf 


M.E. 


Oudin  Transformer 


Fig.  7 


(Courtesy  "Modern  Electrics.") 


One  of  the  important  points  to  be  altered  is  the  spark  gap  connected  into  the 
exciting  transformer  secondary  circuit.  This  has  a  tendency  to  arc  and  so  destroy 
any  chance  of  the  condenser  discharge  in  the  gap  being  quickly  or  disruptively  wiped 
out.  This  is  due  to  the  heating  of  the  air  in  the  gap,  owing  to  the  heavy  currents 
traversing  it  in  large  sets.  One  way  of  reducing  the  arcing  and  heating  of  the 
disruptive  spark  gap,  is  to  place  several  ball  gaps  in  series,  the  number  dependin  i 
upon  the  size  of  the  set,  but  about  4  to  6  being  sufficient  for  transformers  of  less 
than  one  kilowatt  capacity. 

The  series  gap,  is  not  the  best  solution  of  the  problem,  however,  and  the  rotatins 
or  rotary  spark  gap  has  finally  been  found  the  best,  this  type  consisting  of  a  disc  of 
hard  rubber  about  8  or  10  inches  in  diameter,  mounted  upon  the  shaft  of  a  small 
1-16  H.  P.  alternating  or  direct  current  motor,  capable  of  running  at  a  speed  of 
1,500  revolutions  or  more  per  minute.  The  disc  has  a  number  of  projecting  zinc 


134 


WIRELESS  COURSE— LESSON  NO.  17 


or  brass  plugs  mounted  on  one  flat  face,  the  plugs  being  spaced  about  one  inch  apart, 
and  all  connected  together  electrically.  The  spark  takes  place  between  two  dia- 
metrically opposite  plugs  and  two  stationary  electrodes. 

The  advantages  due  to  this  gap  construction  are  at  once  apparent.  A  fresh 
supply  of  cool  air  is  kept  constantly  passing  through  the  gaps,  and  the  rotating  disc 
also  acts  as  a  fan  cooling  the  electrodes  mounted  upon  it.  In  some  forms  of  the 
rotary  gap,  only  one  spark  gap  is  utilized,  one  of  the  wires  connecting  to  the  rotating 
plugs  through  a  spring  contact  or  brush. 

The  condensers  used  for  large  Tesla  sets,  are  generally  of  the  glass  plate  type, 
as  this  form  possesses  many  advantages  over  leyden  jars,  one  of  them  being 
the  more  flexible  adjusting  of  the  circuit,  as  the  capacity  is  divided  up  into  a 
number  of  sections,  any  of  which  may  be  used  as  required. 

The  transformers  utilized  to  charge  the  condensers,  in  high  powered  sets  of  this 
character,  are  either  wax  impregnated  or  oil  immersed.  The  primary  windings  are 
made  for  any  voltage  from  110  to  550  A.  C.  60  or  120  cycles,  ordinarily.  The  secondary 
windings  are  sometimes  arranged,  so  that  anywhere  from  10,000  to  20,000  volts,  can 
be  obtained,  according  to  the  connection  of  the  various  sections  composing  it.  The 
variation  of  the  secondary  voltage  is  also  made,  by  arranging  the  primary  winding 
or  coil  in  several  steps  or  sections,  the  usual  method  being  to  bring  out  taps  from 
succeeding  turns  or  layers,  to  the  number  of  six  or  more. 

The  Tesla  or  Oudin  coils,  employed  for  large  sets,  ito  step  up  the  voltage  of  the 
circuit,  are  invariably  of  the  air  insulated  type.  An  Oudin  coil  is  not  very  different 
from  a  Tesla  coil,  except  that  the  primary  and  secondary  coils  are  connected  in  another 
way.  This  is  illustrated  by  the  diagram  fig.  7,  which  shows  how  tthe  bottom  of  the 
primary  winding  is  joined  to  the  bottom  of  the  secondary  coil,  the  high  frequency 
sparks  being^  taken  from  the  ball  at  the  top  of  the  secondary.  In  the  construction 
of  the  Oudin  coil,  which  is  used  principally  for  lecture  and  Electro-therapeutical 
requirements,  the  primary  coil  is  placed  at  one  end  of  the  secondary  coil,  and  not 
in  the  centre,  as  in  the  regular  Tesla  coil. 


— vAAM/V — 


LIMIT  OF   ATMOSPHERE 


a 


— -  w    er 


Fig.  8 


The  high  frequency  coils,  whether  Tesla  or  Oudin,  are  made  with  a  primary 
winding  of  a  few  turns,  says  10  to  15  turns,  of  large  stranded  or  solid  copper  conductor, 
spacing  the  turns  quite  a  distance  apart.  The  secondary  .windings  are  composed 
of  800  to  1,000  turns  of  fine  copper  wire,  with  a  small  space  equal  to  the  thickness 
of  the  wire  between  turns,  to  prevent  the  enormous  induced  potentials  in  it  from 
breaking  down  the  coil. 


WIRELESS  COURSE— LESSON  NO.  17 


135 


Tesla,  in  some  of  his  researches  a  few  years  ago,  had  high  frequency  discharges 
developed  to  such  a  degree  that,  in  one  test  he  was  able  to  make  the  current  leap 
a  gap,  twenty-five  feet  long,  the  sparks  being  two  to  three  feet  in  diameter,  and 
accompanied  by  a  roar,  which  could  be  heard  ten  to  twelve  miles  away.  The  voltage 
of  this  discharge  was  up  in  the  billions,  and  the  amperage  800.* 

The  object  of  all  these  experiments  by  Nikola  Tesla,  was  along  his  line  of  work 
regarding  the  wireless  transmission  of  electrical  energy,  for  useful  purposes.  It  may 
seem  like  a  dream  to-day,  but  then  it  is  only  a  little  over  fourteen  years  ago  that 
man  only  dreamed  about  the  wireless  telegraph,  and  at  the  end  of  this  short  space 
of  time,  there  are  laws  passed  which  compel  its  use  on  all  ships  that  travel  the 
high  sea. 

Tesla,  in  his  first  book,  published  over  twenty  years  ago,  advocated  the  cause 
of  the  wireless  transmission  of  energy,  for  the  lighting  of  lamps  and  running  of 
motors,  and  at  that  time,  in  a  lecture  before  the  Institute  of  Electrical  Engineers, 
at  London,  England,  he  demonstrated  wireless  lights  and  a"no-wire"  motor  operating 
over  short  distances. 


Fig.  9 

The  motor  was  operated  by  connecting  one  of  its  coil  terminals  to  earth,  and 
the  other  terminals  to  an  insulated  metal  plate  suspended  in  the  air.  This  was  Tesla's 
theory  on  a  small  scale,  for  the  wireless  transmission  of  energy  to  any  distance. 

The  form  of  the  energy  was  to  be  in  high  frequency  oscillations  stepped  up  to 
many  million  volts,  and  radiated  from  extra  high  aerial  wires,  extending  into  the 
upper  strata  of  rarefied  air,  through  which  the  high  voltage  currents  travel  easily. 

The  aerial  wire  would  of  necessity  be  quite  high,  probably  more  than  50  miles,  so 
as  to  reach  above  the  atmospheric  envelope  surrounding  the  earth,  which  is  variously 
estimated  at  from  30  to  50  miles  thick. 


•See  "Wireless  Telegraphy."  t>y   Bewail. 


136 


WIRELESS  COURSE— LESSON  NO.  17 


The  scheme  for  this  plan  of  distributing  and  utilizing  electrical  energy  is  shown 
by  fig.  8,  where  the  aerial  wires  are  represented  at  A  and  Al,  step-up  transformer  at 
distributing  station  T,  excited  from  the  high  frequency  generator  G,  the  ground  being 
made  at  E. 

The  receiving  apparatus  comprises  the  aerial  wire  A  1,  for  gathering  the  required 
energy  out  of  the  ether,  the  step-down  transformer  T  1,  from  whose  low  voltage 
primary  coil  is  run  the  special  motor  M,  or  lights  and  other  devices  as  desired.  The 
receiving  terminal  ground  is  established  at  E  1. 

Patents  covering  this  scheme,  were  issued  to  Tesla  many  years  ago,  but  for 
several  reasons,  financial,  industrial  and  others,  the  practicability  of  it  has  never  been 
tried  out,  but  however  this  may  be,  it  does  not  mean  that  the  scheme  is  impossible. 

In  fig.  9,  is  illustrated  the  laboratory  and  tower  of  Tesla's  wireless  plant  on  Long 
Island.  The  high  frequency  discharge  with  the  Tesla  apparatus,  aforementioned,  is 
seen  in  cut  No.  10. 

From  the  foregoing  it  is  easy  to  understand  that  there  is  probably  no  more  inter- 
esting or  remunerative  field  of  electrical  research  than  that  of  high  voltage  and  high 
frequency.  Its  wonders  are  unending,  and  very  little  of  practical  value  is  known  about 
it  to-day. 

Electrical  engineers  have  been  too  busy  developing  and  applying  the  ordinary 
forms  of  alternating  and  direct  current  for  useful  purposes.  But  they  are  now  begin- 
ning to  realize  that  the  Tesla  currents  possess  some  hitherto  unknown  qualities,  and 
that  they  are  to  play  an  important  role  in  the  realm  of  electrical  activities  in  the 
years  to  come. 


Fig  10 

Amateurs  and  experimenters  along  wireless  and  scientific  lines  have  wonderful 
opportunities  open  before  them,  if  they  could  but  realize  it.  Upon  the  shoulders  of 
the  present  clay  youthful  electrical  student  in  his  attic  laboratory  will  rest  the  work  of 
developing  the  future  electrical  inventions  and  problems.  So  if  they  are  alert,  as  many 
of  them  are,  they  will  build  up  their  early  education  well,  for  the  electrical  field  is  no 
longer  a  habitat  for  the  unknowing  mind.  Brains,  and  plenty  of  it,  coupled  to  practical 
research  in  field  and  laboratory  are  the  potent  factors  in  the  dawning  electrical  era. 

Be  not  satisfied  to  simply  punch  the  wireless  key  or  throw  in  a  switch  but  make 
it  your  personal  business  to  ascertain  the  why  and  the  wherefore  of  each  action  and 
phenomenon.  Experiment  and  study,  and  the  world  is  yours. 


WIRELESS  COURSE— LESSON  NO.  18 


137 


Lesson  Number  Eighteen 

THE  WIRELESS   TELEPHONE. 

E  wireless  telephone,  unlike  its  twin  brother,  the  radio-telegraph,  does  not 
require  the  mastery  of  any  codes  to  become  of  value  to  mankind,  and  so 
naturally  would  be  the  ideal  system  of  communicating  without  wires. 

However  this  may  be,  it  has  not  kept  pace  with  the  wireless  telegraph,  in  the 
distance  signalled  over,  the  telegraph  having  successfully  covered  3,000  to  4,000  miles 
frequently,  and  Marconi  claims  to  have  received  a  message  5,600  miles.  The  maximum 
distance  to  which  radiophone  speech  has  been  carried  does  not  exceed  a  few  hundred 
miles,  and  this  only  at  certain  rare  intervals,  during  experimental  tests.  There  are 
hundreds  of  wireless  telegraph  stations  in  daily  commercial  operation  now,  while 
there  is  not  one  radiophone  station  in  commercial  service. 

To  be  able,  to  pick  up  an  ordinary  telephone  transmitter,  talk  into  it,  and  propa- 
gate the  spoken  word  a  distance  of  a  thousand  miles  or  more;  that  has  been  the 
dream  and  ambition  of  many  learned  men  in  all  ages,  ancient  as  well  as  modern. 
But  how  to  do  it  was  another  story,  and  still  remains  so. 

It  was  thought,  when  wireless  telegraphy  became  prominent  a  few  years  ago, 
that  it  would  be  a  comparatively  easy  matter  to  talk  or  telephone  over  the  sayhe 
distances  that  the  telegraph  signals  covered  so  readily,  and  undoubtedly,  when  the 
proper  method  of  propagating  the  speech  through  the  ether  is  found,  the  same  dis- 
tances can  be  covered. 

Like  every  other  branch  of  science,  the  original  investigators  are  few  and  far 
between.  The  general  trend  of  radiophone  researches  thus  far,  have  shown  this 
in  no  small  degree.  If  one  experimenter  employs  an  arc  lamp  to  generate  the  neces- 
sary undamped  oscillations  with,  then  all  the  rest  must  putter  around  with  a  similar 


wvw- 

AA/V 


1. 


Fig.  1 


(Courtesy  "Modern   Electrics.") 


device,  in  the  meanwhile  unloading  a  few  million  dollars  worth  of  "WIRELESS 
TELEPHONE"  stock  on  an  unsuspecting  public.  This  was  the  course  followed 
by  the  Radio  Telephone  Company,  which  is  now  extinct,  as  are  also  the  Collins 
Wireless  Telephone  Company,  and  a  number  of  others  who  sprung  up  over  night. 
Both  of  these  loudly  heralded  systems  used  an  electric  arc  to  talk  with,  but  they 
only  talked  when  the  arc  felt  so  inclined,  and  not  very  far  at  that.  From  the  very 


Copyright  1912  by   E.   I.   Co. 


138 


WIRELESS  COURSE— LESSON  NO.  18 


nature  of  an  electric  arc,  which  is  unstable  and  constantly  changing,  it  is  evident 
that  it  is  not  the  proper  device  for  commercial  radiophony. 

The  simplest  form  of  a  wireless  system  for  transmitting  articulate  speech,  but 
only  good  for  distances  not  exceeding  50  feet,  is  depicted  by  the  drawing  of  fig.  1, 
where  P  and  S  are  coils  of  insulated  wire,  about  six  feet  in  diameter,  with  40  to  SO 
turns  of  No.  18  B.  &  S.  gauge  wire  on  the  transmitting  coil,  and  80  to  100  turns  of 
N-o.  28  gauge  wire  on  the  receiving  coil  S. 

At  H,  is  connected  a  small  induction  coil,  such  as  used  in  medical  sets,  with  a 
paper  and  tin  foil  condenser  at  C,  telephone  transmitter  M,  and  a  battery  of  8  to  10 
dry  cells  or  a  storage  battery. 


(Courtesy  "Modern   Electrics.")  Fig.  2 

The  receiving  coil  S,  is  connected  to  a  telephone  receiver,  the  more  sensitive  the 
better.  The  ground  connections,  .indicated  by  the  dotted  lines,  are  said  to  improve 
the  results. 

The  operation  of  this  inductive  wireless  telephone  set,  is  on  the  same  order 
as  that  existing  between  the  primary  and  secondary  coils  of  an  induction  coil  or  trans- 


•Oh 


(Courtesy  "Modern   Electrics.") 


Fig.  2a 


former,  or  purely  electro-magnetic  induction,  and  consequently  quite  feeble  in  its 
sphere  of  usefulness.  It  makes  a  good  demonstration  set  for  talking  through  stone 
walls  and  the  like,  having  actually  been  used  by  the  Collins  Company  to  sell  stock 
with  at  the  Philadelphia  Electric  Show  in  1908. 

Another  very  simple  wireless  telephone,  working  on  the  conduction  theory  in- 
stead of  the  induction  theory,  is  shown  by  the  diagrams  figs.  2  and  3.*  The  trans- 
mitting station  is  represented  at  fig.  2,  and  comprises  a  microphone  transmitter  M, 
a  battery  of  several  cells  B,  a  zinc  plate  Z,  and  a  copper  plate  C;  the  zinc  plate 
being  buried  about  3  feet  below  the  surface  of  the  earth,  and  the  plate  C  about  IS 
feet  deep  in  the  earth. 

*See  "The  Wireless  Telephone,"   by   H.   Gernsbaek,   page  25.     (E.   I.  Co.,  25  cents.) 


WIRELESS  COURSE— LESSON  NO.  18 


139 


The  receiving  station  has  the  same  construction,  only  the  copper  plate  C  1,  is 
buried  15  feet  deep,  and  opposite  the  zinc  plate  C,  of  the  transmitter.  Insulated 
wires  lead  up  from  the  buried  plates  to  the  instruments.  Around  the  ground  plates 
was  placed  some  saturated  solution  of  chloride  of  zinc,  to  keep  the  earth  moist,  and 
also  to  set  up  an  electrolytic  action  between  the  plates. 

Hugo  Gernsback  says  this  scheme  worked  very  well,  up  to  three  miles  between 
the  stations,  when  the  plates  at  each  station  were  separated  300  yards. 

Such  systems  as  these  are,  of  course,  limited  in  their  field  of  action,  as  regards 
practicability,  and  so  several  schemes  for  propagating  speech  over  long  distances  have 
been  evolved. 


Fig.  3 


(Courtesy  "Modern  Electrics.") 


The  first  principle  involved  in  long  distance  radiophony  by  means  of  electro- 
magnetic waves  set  up  in  the  ether,  is  that  the  waves  set  up  for  this  purpose,  must  be 
those  due  to  undamped  oscillations  of  great  frequency  The  oscillations  generated 
in  an  ordinary  wireless  telegraph  transmitter,  are  highly  damped  and  follow  a  curve 
similar  to  that  in  fig.  3,  while  an  idea  of  an  undamped  oscillation  appears  at  fig.  4. 

w.A/wm 


Fig.  4 


(Courtesy  "Modern  Electrics.") 


It  has  been  found  that  for  good  radiophony,  the  oscillations  generated  must  be 
undamped  or  of  constant  amplitude,  and  also  that  they  must  have  a  frequency  or 
periodicity  of  not  less  than  40,000  cycles  per  second,  otherwise  the  speech  will  be 
broken  or  harsh,  due  to  the  ear  perceiving  the  alternations  of  the  talking  circuit. 


vwww- 

Ri 


c 


Fig.  5 

There  are  two  methods  in  general  use  now,  for  the  production  of  undamped 
alternating  currents  with  a  frequency  of  at  least  35,000  cycles  per  second,  one  being 
that  involving  the  use  of  an  electric  arc,  and  the  other,  the  direct  generation  of 
such  a  current  by  means  of  an  alternating  current  dynamo,  rotated  at  tremendous 
speeds,  which  sometimes  reach  30,000  R.  P.  M. 

The  arc  method  wiill  be  described  first,  as  it  was  the  first  to  be  employed  for 
wireless  telephony. 

The  arc  scheme  of  producing  undamped  high  frequency  oscillations  dates  back 
to  the  discovery  of  the  musical  arc  by  Dudcll,  in  1900.  Dudell's  arrangement  is  given 
at  fig.  5,  where  S  is  an  ordinary  solid  carbon  arc,  C  a  condenser  of  about  3  micro- 


140 


WIRELESS  COURSE— LESSON  NO.  18 


farads,  and  the  inductance  of  helix  L  is  of  5  milli-Henries.  The  arc  was  fed  by  a 
direct  current  dynamo,  G,  delivering  42  volts  pressure,  R  and  R  1  are  inductive  re- 
sistances. 

The  action  of  the  capacity  and  inductance  shunted  across  the  arc  has  been  de- 
scribed as  follows: — 

With  a  steadily  burning  arc  S,  shunted  by  a  capacity  C,  and  inductance  L,  the 
capacity  will  instantly  take  upon  itself  a ,  charge,  and  the  current  through  the  arc  is 
simultaneously  diminished  or  made  smaller;  ithe  potential  difference  across  the  arc 
therefore  increases,  and  this  tends  further  to  charge  the  condenser.  This  now  reacts 
on  the  arc,  still  further  augmenting  its  current,  which  in  turns  lowers  the  potential 
difference. 

As  it  discharges  through  an  inductance  L,  it  not  only  fully  discharges,  but  be- 
comes charged  in  the  opposite  direction,  just  as  a  pendulum,  when  pulled,  to  one  side 
and  released,  will  not  only  go  back  to  its  original  position,  but  far  beyond  it  in  the 
opposite  direction. 

When  in  'this  condition,  it  is  ready  to  repeat  the  operation  with  more  vigor  than 
before,  and  so  persistent  and  undamped  oscillations  are  set  up  by  the  condenser 
charging  and  discharging.  To  have  the  arc  emit  a  musical  note,  it  is  positively  es- 
sential that  the  inductance  and  capacity  be  properly  adjusted  to  each  other,  other- 
wise the  oscillations  produced  will  be  feeble  and  weak. 

After  the  discovery  of  the  Dudell  musical  arc,  a  Danish  scientist,  Mr.  Valdemar 
Poulsen,  developed  a  special  arc  for  radiophonic  purposes,  which  employed  one  solid 
carbon  electrode  and  one  metallic  water  cooled  electrode. 

With  this  arrangement,  Poulsen  was  able  to  produce  powerful  undamped  high 
frequency  oscillations,  with  a  periodicity  of  from  500,000  to  1,000,000  cycles  per  sec- 
ond, which,  of  course,  were  highly  suitable  for  wireless  telephony.  This  arc  was 
burned  in  a  chamber  filled  with  hydrogen  vapor,  formed  by  admitting  alcohol  drop 
by  drop,  and  allowing  it  to  become  vaporized  by  the  heat  of  the  arc  itself.  In  the 
perfected  Poulsen  radiophone  arc  apparatus,  the  carbon  electrode  is  rotated  by  a 
motor  and  a  very  strong  magnetic  field  is  concentrated  upon  the  arc  proper. 


(Courtesy  "Modern   Electrics.") 


In  the  wireless  telephone  system  developed  by  A.  Frederick  Collins,  of  Newark, 
N.  J.,  a  rotating  arc  was  the  medium  by  which  the  undamped  high  frequency  oscilla- 
tions were  produced.  The  Collins  Company  claimed  to  have  talked  from  Newark  to 
Philadelphia,  an  air-line  distance  of  about  90  miles  with  their  system. 

The  Collins  oscillating  arc  is  quite  an  ingenious  device,  and  instead  of  employing 
carbon  or  metal  rods,  there  are  used  two  constantly  rotating  discs  of  carbon-graphite, 
which  are  capable  of  being  moved  toward  or  away  from  each  other.  This,  it  will  be 
seen,  provides  a  constant  uniform  electrode  face,  and  an  arc  of  great  constancy  can  be 
maintained  between  the  two  disc  edges,  besides  being  very  well  cooled  and  ventilated. 


WIRELESS  COURSE— LESSON  NO.  18 


141 


The  arrangement  of  it-he  complete  sending  and  receiving  apparatus  used  in  the 
Collins  radiophone  system,  is  illustrated  by  the  diagram  fig.  6.  The  various  parts  are 
clearly  shown,  and  require  but  little  explanation. 

The  rotating  arc,  is  burned  between  two  large  blow-out  electro-magnets,  and  the 
arc  current  is  5000  volts  D.  C.  supplied  by  a  high  tension  D.  C.  dynamo.  The  varia- 
tions in  the  arc  oscillations  are  made  by  a  microphone  transmitter,  connected  up  with 
25  volts  D.  C.  in  the  primary  circuit  of  the  induction  coil  shown.  Its  secondary  wind- 
ing induced  currents,  follow  the  variations  of  the  primary  current,  and  are  superim- 
posed across  the  arc,  through  the  condenser  shown,  which  prevents  the  arc  D.  C. 
from  shunting  back  through  the  induction  coil  secondary  and  burning  it  out. 

To  ascertain  when  the  maximum  activity  occurs  in  the  arc's  production  of  un- 
damped oscillations,  the  vacuum  or  resonance  tube  is  utilized,  both  electrodes  in  it 
glowing  brightly  and  evenly  when  the  proper  amount  of  capacity  and  inductance  are 
shunted  around  the  arc. 

The  undamped  oscillations  set  up  by  the  arc,  are  stepped-up  to  a  very  high 
potential,  by  means  of  the  auto-transformers  or  helices  shown  in  diagram. 


Fig.  7 

The  Collins  receiving  set,  includes  a  special  thermo-electric  detector  of  two  fine 
crossed  wires,  high  resistance  telephone  receivers,  variable  condensers,  tuning  in- 
ductances, aerial  and  ground.  The  ordinary  wireless  telegraph  receiving  station  is 
often  used  for  receiving  radiophone  talk,  a  good  detector  to  use  being  the  penoxide 
of  lead,  Perikon  or  the  Audion,  which  is  the  best  of  all. 

The  other  method  of  producing  undamped  oscillations  for  radiophony  is  the 
electro-dynamic  way,  as  followed  by  Prof.  Fessenden,  formerly  special  wireless  scien- 
tist for  the  U.  S.  Government.  The  special  high  frequency,  25  to  30  volt,  alternator 
used  by  him,  rotates  at  terrific  speed  and  develops  a  constant  alternating  current  of 
over  30,000  cycles  per  second,  so  that  no  interruptions  in  the  transmitted  speech  is 
heard  whatever. 


142 


WIRELESS  COURSE— LESSON  NO.  18 


The  commonest  manner  in  which  this  alternator  is  connected  to  the  aerial  is 
depicted  in  fig.  7,  where  A  is  the  aerial,  G  the  alternator,  T  the  transmitter,  and  E 
earth.  In  other  words,  the  alternator  and  transmitter  are  in  series. 

The  transmitter,  when  spoken  into,  serves  to  vary  the  current  strength  in  the 
circuit,  owing  to  its  change  in  resistance,  and  this  causes  a  corresponding  variation 
in  'the  strength  of  the  ether  waves  set  up,  and  when  these  varying  etheric  waves  im- 
pinge upon  the  receiving  aerial,  they  are  transformed  into  high  frequency  oscillatory- 
currents  surging  through  the  aerial  system,  and  are  interpreted  by  proper  receiving 
instruments. 


T 


I 

0 


o  0 

Fig.   8  (Courtesy   "Modern   Electrics.")  Fig.   9 

The  Fessenden  receiver  recently  perfected,  and  termed  by  him  the  Heterodyne, 
is  a  type  of  polarized  receiver. 

Having  once  devised  a  method  of  producing  the  necessary  radiophone  transmit^ 
ting  current,  the  problem  that  remained  and  does  remain  in  great  part  yet,  was  the 
manner  of  controlling  the  strength  of  the  current,  when  the  transmitter  was  spoken 
into. 

The  ordinary  carbon  grain  microphone  transmitter  soon  heats  up,  when  any- 
thing over  a  fraction  of  an  ampere  is  put  through  it.  So  it  became  necessary  to 
invent  another  type,  capable  of  handling  several  amperes  if  need  be. 

One  of  the  most  ingenious  of  these  and  at  the  same  time  most  efficient,  is  that 
envolved  by  Prof.  Majorana,  an  Italian  inventor.  A  view  of  this  transmitter,  of  the 
"hydraulic  microphone"  type,  is  shown  at  figs.  8  and  9. 

At  T,  in  the  drawings  is  a  tube  containing  water  or  other  liquids,  which  tends 
to  flow  downward  through  the  constricted  portion  G,  in  a  fine  stream,  but  after 
flowing  thus  for  a  short  distance,  it  breaks  up  into  drops.  Now,  if  the  tube  T,  re- 
ceives a  sudden  shock,  the  breaking  up  of  the  liquid  stream  is  greatly  facilitated, 
shortening  the  stream  proper,  according  to  the  force  of  the  shock. 

This  shocking  of  the  tube  was  found  to  be  suitable,  when  due  to  different 
sounds,  as  of  the  voice,  inside  the  tube,  and  thus  it  was  that  Prof.  Majorana 
succeeded  in  making  the  water  column  act  in  unison  with  the  air  vibrations  set 
up  by  the  spoken  voice. 


WIRELESS  COURSE— LESSON  NO.  18 


143 


His  arrangement  for  the  working  transmitter,  is  depicted  at  fig.  9,  in  which 
B  and  C,  are  two  fine  wires,  inserted  into  the  stream  of  liquid,  and  the  variation  in 
the  resistance,  due  to  the  changing  of  the  streams  shape,  when  acted  upon  by  the 
transmitter  diaphragm  A,  causing  the  transmitting  current  to  vary  simultaneously 
and  proportionately. 


r 


Fig.  10 


Fig.  11 


Fig.  12 


(Courtesy  "Modern  Electrics.") 


Another  part  of  the  scheme  in  this  transmitter  is  that  the  conductivity  of  the 
liquid  stream  may  be  varied  by  making  it  of  some  different  solution,  such  as  salt 
water,  mercury,  etc. 

Thus,  the  wireless  telephone,  which  seemed  to  promise  so  much  at  first,  has  not. 
up  to  the  present  lime,  come  into  its  own,  owing  principally  to  the  fraudulent  cor- 
porations promoting  it,  or  rather  who  claimed  to  be  promoting  it.  However,,  the 
future  is  full  of  promise  for  it,  and  it  is  bound  to  come  some  time,  and  quite  pos- 
sibly will  be  a  strong  rival  of  the  regular^wire  companies. 

Mr.  Poulsen's  new  wireless  station  near  Lyngby,  not  far  from  Copenhagen,  has 
been  completely  remodeled  lately.  (See  also  Lesson  No.  7.) 

This  station  is  the  more  interesting  because  nearly  all  recent  inventions  of  Mr. 
Poulsen,  in  Wireless  Telephony,  have  been  made  here. 

The  aerial  net  is  now  70  meters  (1m.  =  39.37  inches)  high  against  37  meters 
original  height. 

Two  masts  about  90  meters  apart,  fig.  10,  carry  the  aerials  downward.  The 
electrical  counterweight  is  a  wire  net  which  is  stretched  horizontally  over  the  ground, 
a  few  feet  away  from  it. 

A  gasolene  engine  of  20  H.  P.  drives  the  dynamo,  which  supplies  the  arc-genera- 
tor. The  output  of  the  dynamo  is  10  K.  W.  at  500  volts. 


144 


WIRELESS  COURSE— LESSON  NO.  18 


As  will  be  known  the  Poulsen  system  uses  undamped  oscillations  (similar  to  the 
De  Forest  system)  produced  by  means  of  an  electric  arc  operated  in  hydrogen  gas. 
No  spark  coil  or  oscillator  balls,  etc.,  as  in  the  common  wireless  stations  arc  found 
here,  and  what  strikes  one  most  is  the  absence  of  complicated,  elaborate  apparatus, 
and  instruments. 

The  generator  comprises  only  one  arc  which  in  addition  is  actuated  upon  by  a 
strong  magnetic  field. 

The  positive  electrode  of  the  arc  is  of  copper,  the  negative  of  carbon.  If  more 
than  6  K.  W.  are  used  the  copper  anode  is  constantly  cooled  by  means  of  water  cir- 
culation through  the  interior  of  the  electrode. 

The  new  station  has  not  yet  been  tested  for  its  maximum  distance,  but  has  kept 
up  communication  with  other  stations  as  far  as  2,500  kilometers  (1,560  miles)  away. 
Mr.  Poulsen  is  quite  confident  that  his  station  can  reach  3,000  kilometers  easily.  The 
wave  length  in  long  distance  tests  was  usually  1,200  meters.  A  30  K.  VV.  Poulsen 
arc  has  sent  telegraphic  signals  6,000  miles,  from  the  Arlington,  W.  Va.,  station,  to 
Honolulu,  T.  H. 


POULSEN    IN    HIS    WIRELESS    STATION. 

(Courtesy  "Modern   Electrics.") 

The  undamped  oscillations  also  have  another  big  advantage.  It  is  now  possible 
to  receive  from  2-4  messages  on  the  same  antenna  and  good  operators  can  work  with 
less  than  1%  difference  of  the  wave  length. 

Fig.  11  shows  the  interior  of  the  station.  Of  interest  is  the  hard  rubber  window 
with  lightning  arrester,  through  which  the  aerial  is  led.  This  is  seen  on  the  right- 
hand  side  of  the  picture,  near  the  ceiling  of  the  room.  Another  similar  window  (close 
to  the  top  of  the  table)  carries  the  wire  to  the  electrical  counterweight. 

The  receiver  is  shown  at  the  left-hand  side. 

Fig.  12  gives  a  good  view  of  the  generator,  and  also  shows  the  peculiar  high  ten- 
sion- discharge  on  the  resonator. 

A  new  idea  has  lately  been  incorporated  in  the  generator.  Instead  of  complicated 
apparatus  for  the  production  of  the  hydrogen,  alcohol  is  used  which  is  introduced  by 
letting  it  drop  slowly  in  the  arc  chamber.  One  to  two  drops  per  second  are  sufficient 
for  a  load  of  1  K.  W. 

It  is,  of  course,  understood  that_if  desired  this  station  can  be  used  for  wireless 
telephony,  by  merely  throwing  over  a  switch. 


pi 

WIRELESS  COURSE— LESSON  NO.  19  145 

Lesson  Number  Nineteen. 


THE  MATHEMATICS   OF  WIRELESS   TELEGRAPHY. 

E  art  oi  wireless  involves  the  use  of  some  oi  the  finest  developments  in  the 
realm   oi   mathematics,    for   some   of  the   calculations,    but   only   the   more    im- 
portant practical  formulae  will  be  treated  on  here,  as  they  will  most  likely  meet 
the  needs  of  the  student  or  operator. 

CALCULATION  OF  WAVE-LENGTH. 

The  calculation  of  wave-length,  i.  e.  the  length  of  the  ether  wave  emitted  from 
the  aerial  wire  in  transmitting,  is  frequently  desired  to  be  known.  The  best  way  is  to 
employ  a  wave-meter,  correctly  calibrated. 

For  untuned  sending  circuits,  with  straight  vertical  aerials,  the  wave-length  has 
been  ascertained  to  be  very  close  to  4.5  times  the  length  of  the  aerial  wire  from 
spark  gap  to  its  outer  end  when  the  spark  gap  is  close  to  the  ground. 

In  tuned  sending  sets,  the  wave-length  emitted  from  the  transmitting  circuit 
is  given  by  the  equation  below: 


W  =  TT  2  V  V 


Or     W  =  1,884,960,000  V  L.  C  ; 

Where; —  W  =  Wave-length  in  meters. 
TT  =3.1416  (a  constant). 
2    =  a  constant. 

V    =  Velocity  of  ether  waves  or  300,000,000  meters  per  second. 
L  is  the  Inductance  in  Henries  of  the  helix  turns. 
C  is  the   capacity  in   Farads   of  the   condenser. 

In  calculating  the  wave-length  it  must  be  noted  that  the  inductance  of  the  helix 
in  the  above  equation,  does  not  mean  the  total  inductance  of  it,  but  only  those  turns 
in  use  in  the  condenser  or  closed  oscillating  circuit,  when  the  set  is  in  tune. 

WAVE  FREQUENCY. 

The  wave  frequency,  or  the  number  of  waves  occuring  per  second  can  be  readily 
computed  from  the  other  constants  when  they  are  known.  Wave  frequency  equals: 

5,033,000 
F  =  — 


V '  L.    C 

Where:  F  is  the  wave  frequency  in  cycles  per  second. 

L  is  the  inductance  of  helix  turns  in  use  in  condenser  circuit,  in  centimeters. 
C  is  the  capacity  of  the  condenser  in  tuned  sending  circuits,  in  microfarads. 

300,000,000 


Also  F= 


Wave  length  in  meters. 


The  term;  1/1,0,    is  called  the  oscillation  constant. 

INDUCTANCE  CALCULATION. 

The  inductance  of  a  single  layer  coil  or  helix  of  wire,  is  calculated  in  centimeters, 
by  the  following  formula: 

L.  =  1  (TT  D  N)  2 
Copyright  1912  by  E.  I.  Co.     •    ' 


146 


WIRELESS  COURSE— LESSON  NOT  19~T*s. 


In  which: — L  is  the  inductance  of  helix  in  centimeters. 
1    is  the  length  of  helix  in  centimeters. 
"IT  =  3. 1416 

D  is  diameter  of  helix  in  centimeters. 

N  is  the  number  of  turns  per  centimeter  Igjigtff  of  helix. 

This  formula  however,  is  subject  to  quite  a  large  error  for  short  fat  helices,  but 
being  correct  to  within  3  per  cent,  if  the  helix  is  50  times  its  diameter  in  length. 

A  pretty  accurate  equation  for  the  helix  inductance  in  C.  G.  S.  units,  evolved  by 
Louis  Cohen,*  is  given  below.  This  formula  is  suitable  for  short  fat  helices  as  well 
as  long  thin  ones,  the  result  being  accurate  to  within  y2  of  1  per  cent,  and  closer  for 
long  ones. 

M*4f 

L.  =  39*796  N2 


^ 

r      2  a4  +  a2!2  Ka3     "I 

V  4  a2  +  I2  ^**8-  _ 


In  which: — La  is  the  inductance  in  absolute  or  C.  G.  S.  units,  (centimeters). 
N  is  the  number  of  turns  per  centimeter  of  helix  length, 
a  is  the   mean  radius  of  helix  in   centimeters. 
1  is  the  length  of  'he  helix  in  centimeters. 

The  value  of  the  inductance  in  Henries,  is  found  by  dividing  La  by  1,000,000,000; 
or  (10)9 

For  helix  lengths  of  not  less  than  15  to  20  times  the  diameter  in  value,  the 
following  formula  holds  good: 

10,028  X  r2  X  N2 


L,    in  Henries  = 


1    X   100,000,000,000 


Where:  r  is  the  radius  of  helix  in  inches. 

N  is  the  total  number  of  turns  on  helix. 
1  is  the  length  of  helix  in  inches. 

CAPACITY  CALCULATIONS. 

The  capacity  of  condensers  may  be  found  approximately  by  the  equation: 

/          2.248   X  K   X   a        \ 
C  =  I  I  H-  1,000,000  ; 

\       t  X  10,000,000,000       / 

Where:  C  is  the  capacity  in   Farads. 

K  is  the  inductivity  of  the  dielectric,  (see  appendix), 
a  is  the  total  active  area  of  dielectric  in  sq.  in. 
t  is  the  thickness  of  dielectric  in  inches. 

To  ascertain  the  capacity  in  micro-farads,  solve  only  that  portion  of  the  equation 
enclosed  in  parenthesis. 

To   find  the  joint   or  total   capacity  of   several   condensers   connected   on  parallel, 
add  their  individual   capacities,   thus: 

Total     C  =  C,  +  C2  +  C3     etc. 

For  the   total   capacity  of  a  number  of  condensers   connected   in   series,  take   the 
reciprocal   of  the   sum   of  their  reciprocals,  thus: 


Total      C  =- 


d  C2  C,       etc. 


*See  U,  S.  Bureau  of  Standard  Record*. 


WIRELESS  COURSE— LESSON  NO.  19  147 

The   required    condenser   capacity    in    micro-farads    for    a   wireless    transformer   of 
certain  size  is: 

Kilowatts   X   10" 
C — 


f    X  v2^ 

Wherein:  f  is  the  frequency  of  transformer  current  in  cycles  per  second. 
V  is  transformer  secondary  volts. 

In  allowing  for  the  secondary  voltage,  Prof.  G.  W.  Pierce,  of  Harvard  University, 
recommends  that  the  figure  of  37,500  volts  per  one  inch  of  spark  be  figured  on,  due 
to  the  heating  of  the  spark  gap,  etc. 

The  formula  below  will  give  the  area  in  square  centimeters  of  active  condenser 
dielectric  required  for  a  certain  capacity: 

36   TT     D     C     10* 
Area  in  Sq.  Cm.  =  „ 

In  which:     TT  =  3.1416 

D  is  the  thickness  of  dielectric  in  centimeters. 
C  is  capacity  required  in  micro-farads. 
K  the  inductivity  factor.  (See  appendix). 
105  equals  10,000 


Ohm's  Law  For  Alternating  Current  Circuits. 

Ohm's  law  as  applied  to  direct  current  circuits  no  longer  holds  good  on  alternating 
current  circuits,  due  to  the  reactive  effects  incurred  by  the  inductance  and  capacity  o; 
the  wires. 

With  resistance,  inductance  and  capacity  in  series,  the  equation  for  current  in 
amperes  is: 

E 
I  in  amperes  = 


2  TT  f  C 

•\ 

Where:  E  is  the  effective  volts. 
R  is  resistance  in  ohms. 
f  is  the  frequency  in  cycles  per  second. 
L  is  the  inductance  in  Henries. 
C  the  capacity  in  Farads. 

TT  equals  3.1416  (a  constant;    representing    the    ratio    between    the    diameter    and 
circumference  of  a  circle.) 

Following    the    same    nomenclature,  this  formula  gives   the  volts   required   to  pro- 
duce a  certain  current  under  like  conditions: 


Volts  =-•--•-        -    -  -  -  l 


Condenser   Charging  Current  On  A.  C.   Circuits. 

When  a  capacity,  in  the  form  of  a  condenser  or  the  inherent  capacity  of  a  con- 
ductor, is  connected  to  an  A.  C.  circuit,  a  certain  current  will  be  required  to  charge 
it.     The  equation  below  gives  the  value  of  this  charging  current  in  amperes: 
Where:  I  is  current  in  amperes. 

E     C     2     TT     f 

1,000,000 

E  effective  voltage. 

C  capacity  in  microfarads. 

f  frequency  of  charging  current. 


148  WIRELESS  COURSE— LESSON  NO.  19 

Primary  Circuit  Calculations. 

In  the  primary  circuit  of  the  sending  transformer,  the  amount  of  power  utilized 
cannot  be  measured  by  a  voltmeter  and  ammeter,  as  in  direct  current  circuits. 
For  incandescent  lamp  loads  only,  this  may  be  nearly  so,  but  not  for  any  inductive 
load  such  as  motors  or  transformers. 

The  energy  in  watts  is  the  product  of  the  volts  and  amperes,  in  a  direct  current  or 
non-inductive  A.  C.  circuit,  but  with  inductive  load  on  A.  C.  circuits,  the  energy  in 
watts  is: 

W=E  I  P; 

Where; — E  is  the  effective  volts;  I  amperes;  and  P  the  power  factor;  but  W  is  the 
actual  or  true  watts  consumed,  not  the  apparent  watts  as  indicated  by  a  voltmeter 
and  ammeter.  Actual  watts  may  be  read  directly  from  a  compensated  direct  reading 
watt-meter,  such  as  the  Weston.  The  power  factor  for  induction  motors  is  about  80 
per  cent;  for  motors  and  lamps  mixed,  90  per  cent;  and  for  transformers  60  to  80 
per  cent;  lamps  alone  100  per  cent.  The  power  factor  is  the  ratio,  (expressed  as  a 
per  cent),  between  the  true  watts,  as  given  by  a  direct  reading  watt-meter,  and  the 
apparent  watts,  or  the  product  of  the  volts  and  amperes.  In  other  words,  the  power 
factor  is  equivalent  to: 

Power  factor-          True  watts 


Apparent  watts 

Also  it  equals  the  cosine  of  the  angle  of  lag  between  the  electromotive  force  and 
the  current. 

The  actual  watts  represent  the  energy  paid  for  by  a  consumer;  not  the  apparent 
watts.  The  difference  between  the  apparent  watts  and  the  true  watts,  constitutes  the 
quantity  known  as  "wattless  current"  or  the  "wattless  component  of  the  circuit," 
and  although  it  has  the  same  heating  effect  in  the  circuit  and  generator  and  motor 
windings  as  direct  current,  it  adds  very  little  to  the  load  on  the  generator. 

Range  Of  Stations. 

The  working  range  of  radio-telegraphic  stations  depends  upon  the  height  of  the 
aerial  wires,  the  radiation  current  in  amperes,  the  wave-length  used,  the  time  of 
operation;  being  approximately  twice  the  normal  day  range  at  night;  and  several 
other  factors,  such  as  the  topography  of  the  land,  the  particular  section  of  the  earth 
signalled  over,  etc.  In  general  it  is  about  twice  as  difficult  to  send  signals  in  hot 
tropical  regions,  as  in  temperate  climates. 

The  actual  working  or  communicating  range  of  'any  station  varies  greatly  and 
cannot  be  wholly  depended  upon,  but  as  long  as  a  conservative  range  is  taken  as  a 
criterion  of  a  certain  station,  based  upon  exhaustive  tests  and  observations,  it  can  be 
pretty  well  relied  upon. 

A  few  years  ago,  during  1909  and  1910,  to  be  exact,  some  very  elaborate  and 
exhaustive  tests  on  long  distance  radio-communication  were  carried  on  between  the 
Brant  Rock  station  of  Prof.  R.  A.  Fessenden,  leased  for  the-purpose  by  the  U.  S. 
Government,  and  the  U.  S.  scout  cruisers,  Salem  and  Birmingham,  the  maximum  dis- 
tances covered  reaching  2,700  miles. 

The  tests  were  under  the  able  supervision  of  Dr.  L.  W.  Austin,  Ph.  D,  of  the 
U.  S.  Naval  Wireless  Telegraphic  Laboratory. 

Dr.  Austin  evolved  an  equation  representing  the  relation  existing  between  received 
aerial  currents,  aerial  altitudes,  transmitting  current  strength,  wave-length  employed, 
and  a  term  known  as  the  absorption  factor,  which  allows  for  the  day  absorption 
caused  by  the  sun's  rays  ionizing  the  upper  strata  of  the  atmosphere  apparently. 

Quantitative  measurements  and  numerous  observations  carried  on  during  the 
tests,  served  to  establish  the  validity  of  this  equation  for  all  distances  up  to  1000 
nautical  miles,  over  salt  sea  water,  in  broad  daylight  with  sun  shining;  for  all  sending 
currents  from  7  to  30  amperes;  aerial  elevations  of  from  37  to  130  feet;  and  all 
wave-lengths  of  from  300  to  3,750  meters. 


WIRELESS  COURSE— LESSON  NO.  19  KQ 

*  OT3  1  ^^2a  ^ 

His  equation  is  as  follows: 


I  =  4.25  -         *•      ."•       "' e  *  -  °'°U15  d 

A   d  ,/ — X 


Where:  I  is  received  aerial  current  in  amperes. 
4.25  a  cons,*,,. 


\ 

l»  to»  I  „.„ 

A  the  wave-length  in  kilometers. 


I8  the  sending  current  in  amperes.  f«   |0|> 

"*  -I  KftT' 


D  the  distance   between  the  stations  in  kilometers. 


rfV-^jJSf^Hp 


hi  elevation  of  transmitting  aerial  in  kilometers. 

A 
ha  elevation  of  receiving  aerial  in  kilometers.  *• 

e  is  the  base  of  the  Naperian  logarithms,  or  2.718281828.  If"    l      iji  faljT- 

0.0015  the  absorption  factor. 

The  conditions  under  which  this  rule  or  formula  was  tested  out  were:  The  trans- 
mitting transformers  were  excited  from  500  cycle  alternating  current  generators,  and 
this  is  very  important  as  a  500  cycle  set  will  send  a  signal  two  or  three  times  as 
far- as  a  low  frequency  set  employing  60  or  120  cycle  primary  current.  The  resistance 
from  the  top  of  the  receiving  aerial,  through  receiving  tuning  inductance,  and  down 
to  the  ground  was  25  ohms.  Ordinary  high  resistance,  Navy  type,  telephone  head 
receivers  and  crystal  rectifying  detectors  were  employed  on  the  long  distance  tests. 

It  was  found  that  when  the  received  aerial  current  did  not  decrease  below  40 
micro-amperes,  (40  millionths  of  an  ampere),  the  communication  was  good  and  also 
regular.  At  a  strength  of  10  micro-amperes,  the  signals  were  just  audible.  Hence  a 
regular  communication  strength  of  current  at  the  receiving  aerial  may  be  taken  at 
40  to  50  micro-amperes. 

This  rule,  good  up  to  1000  nautical  miles,  over  salt  water  in  daytime,  is  the  only 
one  of  any  practical  use  at  the  present  time.  Aside  from  this,  transmitting  sets  oi 
ordinary  low  frequency  type,  will  radiate  messages  at  about  the  following  distances, 
in  daytime  over  land,  in  temperate  zones,  and  a  great  deal  further  over  water  or  at 
night. 

1"  spark  coil,  untuned, 1  to         3  miles 

1"       "        "       tuned, 8  to  15       " 

6"       "        "          " 40  to  50      " 

10"  to  12"  spark  coil,  tuned, 80  to  100 

%    K.   W.   Transformer,    tuned, • 25  to  30      " 

y2    "  "  " 40  to    60    " 

1  "  "  " 80  to    100      " 

2  "  "  "     i 150  to    225      " 

5        "  "  " .....      1000  to  1500      " 

All  the  transformer  sets  used  with  tuned  circuits.  The  distances  cited  are  compiled 
from  data  on  the  performance  of  a  number  of  good  stations,  some  of  them  in  cities, 
where  the  aborption  loss  due  to  ground  leakage  to  roofs  and  wires  are  at  a  maximum, 
and  the  aerials  were  of  good  size,  and  well  insulated.  Thus,  these  figures  will  be 
modified  by  the  height  of  the  aerial,  and  the  kind  of  country  or  water  signalled  over. 
The  figures  above  are  alright  for  transmission  over  water  or  flat  dry  land,  but  where 
mountains  intervene  between  the  sending  and  receiving  stations,  a  decrease  of  pos- 
sibly 50  per  cent,  may  occur  in  the  signalling  range.  Tropical  climates  are  also 
detrimental  to  satisfactory  operation  of  wireless  stations,  and  depreciate  the  normal 
activity  of  a  station  very  considerably,  even  as  much  as  60  per  cent,  in  some  cases, 
in  which  event  it  is  necessary  to  employ  extra  high  aerials  and  long  wave-lengths, 
coupled  to  powerful  transmitters. 


150  WIRELESS  COURSE— LESSON  NO.  19 

No  fixed  rule  can  be  laid  down  for  the  height  of  aerial  to  be  utilized  for  a  certain 
station,  the  size  and  height  usually  being  governed  by  natural  conditions  and  the  size 
of  the  set.  Probably  a  good  average  elevation  for  aerials  in  use  with  sets  of  from 
1  to  5  K.  W.  is  about  150  feet.  See  section  on  aerials  for  further  data. 

„  Summary: 

•«-^^ 

«»flfc  general,j^je  wireless  transmission  of  intelligence  is  strongly  on   the  increase 
commercially,  and  it  is  only  a  matter  of  time,  and  a  short  time  at  that,  when  its  sphere 

of  activity  will  be  vastly  greater  and  broader,  both  on  land  and  sea. 

• 

At  present,  it  is  in  the  phase  of  development  which  every  new  art  must  pass 
through,  and  presents  a  golden  opportunity  to  the  scientists  and  experimenter,  who 
are  bent  upon  discovering  the  secrets  it  holds.  This  is  particularly  true  in  regard  to 
the  wireless  telephone,  which  through  apparent  abandonment,  is  left  to  lie  idly  by, 
whereas  it  is  of  the  most  tremendous  importance,  in  virtue  of  the  fact,  that  it  appeals 
to  every  person,  young  or  old,  savage  or  savant.  Everyone  can  talk  over  a  telephone 
instrument,  but  few  there  are,  who  can  or  care  to  bother  with  a  telegraph  and  its 
codes. 

A  few  remarks  will  be  devoted  here  to  the  present  practices  in  the  art  of  radio- 
communication,  as  regards  the  instruments  employed,  Etc., 

It  has  come  to  be  recognized  after  several  years  of  experimental  research,  that  for 
transmitting  messages  by  wireless  telegraphy,  the  high  frequency  spark  or  whistling 
spark,  is  the  most  efficient  in  cases  of  severe  interference  from  other  stations  and 
bad  static  particularly.  The  principal  systems  employing  a  high  frequency  spark  and 
at  present  being  commercially  applied,  are  the;  Fessenden:  Telefunken:  and  Marconi. 

The  spark  employed  by  the  now  defunct  Radio  Telephone  Co.,  was  a  very  shrill 
high  pitched  one,  but  was  obtained  by  means  of  a  quenched  spark  gap,  the  same  as 
the  Telefunken  Go's  spark.  For  radiophone  work  the  Radio  Co.,  utilized  an  arc  of 
special  construction  burned  in  hydrogen  or  other  gas. 

In  the  science  of  radiophony,  Prof.  R.  A.  Fessenden,  claims  to  have  talked  about 
400  miles  from  Brant  Rock  over  sea.  The  Fessenden  system  has  many  commendable 
features  about  it,  both  transmitting  and  receiving,  but  possibly  the  most  meritorious 
part  of  all,  is  the  absolute  and  unfailing  source  of  high  frequency  undamped  oscillatory 
current  so  essential  in  radiophony.  This  current  is  supplied  by  a  very  high  speed 
alternator,  usually  driven  by  a  steam  turbine,  such  as  the  DeLaval,  in  which  speeds  of 
25,000  to  30,000  revolutions  per  minute  are  common.  This  means  of  producing  high 
frequency  undamped  oscillations  is  much  superior  to  the  arc  or  quenched  spark  gap 
method,  as  these  are  very  sensitive  and  do  not  deliver  a  current  of  constant  amplitude, 
as  the  arc  or  spark  is  constantly  changing.  The  capacity  and  inductance  in  arc  or 
quenched  spark  generators  has  to  be  very  carefully  adjusted,  or  else  the  frequency 
and  strength  of  the  undamped  oscillations  produced  will  be  quite  inferior  and  weak. 

The  Fessenden  system  makes  use  of  high  frequency  alternators  as  aforementioned, 
and  the  frequency  of  some  of  them  is  40,000  cycles,  but  at  present  they  are  building 
several  with  a  frequency  of  200,000  cycles  per  second.  Anything  above  35,000  to  40,000 
cycles  per  second  is  suitable  for  radiophony. 

In  the  modern  receiving  stations,  high  resistance  telephone  receivers,  (not  exceeding 
4,000  ohms  generally),  and  crystal  rectifying  detectors,  such  as  the  Perikon,  Pyron  or 
Silicon,  are  in  wide  use.  The  Marconi  Co.,  are  using  a  Fleming  valve,  similar  to  the 
De  Forest  Audion,  which  is  especially  adapted  to  radiotelegraphic  and  radiophonic 
communication,  due  to  several  inherent  characteristics  it  possesses,  which  enhance 
its  value  greatly  where  much  static  and  interference  have  to  be  worked  through.  Its 
receiving  range  seems  to  compare  favorably  with  that  of  any  other  detector  at 
present  employed,  and  its  smooth  operation  has  gained  it  many  friends,  especially  for 
experimental  research. 

The  tuning  of  the  transmitting  and  receiving  instruments  with  the  aerial  is  now 
done  practically  altogether,  with  two-coil  oscillation  transformers  or  loose-couplers, 
as  the  tuning  in  this  way  is  much  sharper  and  better  defined,  than  with  a  close-coupled 
or  auto-transformer,  with  which  it  is  difficult  to  radiate  a  single  peak  wave,  which 
carries  the  greatest  distance  and  is  the  most  selective  in  tuning. 


WIRELESS  COURSE— LESSON  NO.  19  151 

An  Appendix  of  useful  tables  of  wire  data,  Etc.,  are  added  below  for  the  benefit  of 
the  student. — 

APPENDIX. 
Inductivity  Values  for  Different  Dielectrics. 

Inductivity  Value, 
Dielectric  "K" 

Air  at  Ordinary  Pressure,  Standard   1.0000 

Manila   Paper    1.50 

Paraffine,  Clear  1.68      to  2.32 

Beeswax 1.86 

Paraffine  Wax  1.9936  to  2.32 

Paraffined  Paper  3.65 

Resin 1.77      to  2.55 

Petroleum     2.03       to  2.42 

Hard  Rubber  (Ebonite)   2.05       to  3.15 

Turpentine    2.15       to  2.43 

India  Rubber,  Pure   2.22       to  2.497 

Sulphur    2.24      to  3.84 

Gutta  Percha 2.46      to  4.20 

Shellac   2.74      to  3.60 

Olive  and  Neats-Foot  Oils 3.00      to  3.16 

Sperm  Oil  3.02       to  3.09 

Glass   (Common)    3.013     to  3.258 

Mica  Sheet,  Pure  4.00       to  8.00 

Porcelain  4.38 

Quartz    4.50 

Flint  Glass,  Very  Light   6.57 

"      Light 6.85 

"         "       Very  Dense    •_•  •  • 7.40 

Double  Extra  Dense  .  10.10 


TABLE  OF  DEFLECTIONS  AND  TENSIONS  FOR  ALUMINUM  WIRE. 

D=deflection  in  inches  at  center  of  span;  F=factor,  which  multiply  by  weight  of  foot 

of  wire  to  obtain  tension;  maximum  load=15,000  pounds  per  square  inch;  T=item- 
perature  at  which  wire  is  strung. 

T=— 20°  —10°                       0°                   10°                  20°                 30° 

Span         F           D  FD           FDFDFDFD 

80      12940          34  1660        5?4      1176        8%       961      10          833     11%       781      12% 

100      12940        iy&  2083        7%       1470       10%      1202      12%      1042      143%       933      16 

120      12940        ls/8  2500        8%      1768      12%      1400     153%      1251     17%      1120     19% 

150      12940        2s/8  3038      11%      2540       14%      1788      18%      1552     2134      1390     24 

175      12940        3%  3643      12%      2576      17%     2104     2134     1822     25%      1630     28% 

200      12940        4%  4206      14%      2947      2Q]/&     2403     2V/*     2084     2834      1930     31  % 

T=40°  50°                       60°                   70°                  80° 

F           D  FD           FDFDFD 

680      14%  630      15%        589      16%       555      173%       527     18% 

869      1734  768      19           735      203/6       695     21%       658     2234 

1022      21  %  946      22%        885      24%       835     25%       792     27% 

1265      26%  1177      28%      1060      303%     1039     32%       987     34% 

1488      30%  1377      33%      1279      35%      1215     3734      1152     39%      1099     4134 

1672      35%  1574      38%      1473      4034     1393     43         1316     45%     1256 


152 


WIRELESS  COURSE— LESSON  NO.  19 


COIL  WINDING  FORMULAE. 

The  wave  length  capacity  of  any  tuning  coil  is  given  by  the  following  formula: 

3.1416  x  d  x  t  x  1  x  4 


W.  L.  = 


3.3 


Where: — W.  L..=Wave  length  in  meters. 

d=Diameter  of  coil  in  feet. 

t=No.  of  turns  of  wire  per  inch. 

l=Length  of  coil  in  inches. 
The  No.  of  turns  of  wire  per  inch,  may  be  taken  from  the  wire  table. 

To  find  the  gauge  No.  of  enameled  wire  with  which  to  wind  an  electro-magnet, 
having  given  the  dimensions  of  the  magnet  and  the  resistance  of  the  winding. 

For  example:  Let  the  outside  diameter  of  the  coil  in  inches  be  represented  by  D 
(for  this  case  2");  the  inside  diameter  of  the  coil  by  Dl  (here  1")  and  the  length  of  shell 
by  L  (here  2");  Resistance  of  winding  by  R  (here  say  200  ohms).  Rc=Resistance  per 
cubic  inch  winding;  see  wire  table.  The  formula  is: 


R  = 


Rc  X  TT   X  L   X   (  D'  —  D1 ) 


Then  200 


RcXTTX2X(4-l) 

-  =  4.7124   X   Rc  ;    and  Rc  = 


200 
4.7124 


=  42.44 


TT=3.1416    (a  constant) 

Looking  at  the  enameled  wire  table  the  nearest  value  is  found  to  be  44.9  for  Rc  and 
opposite  this  is  No.  29  wire,  the  size  to  be  used  on  the  magnet. 

TABLE  OF  SPARKING  DISTANCES 
In  Air  for  Various  Voltages  Between  Needle  Points. 


Volts 

5000 
10000 
15000 
20000 
25000 
30000 
35000 
40000 
45000 
50000 


Distance 

Inches.  Centimeter 

.225 

.57 

.470 

1.19 

.725 

1.84 

1.000 

2.54 

1.300 

3.30 

1.625 

4.10 

2.000 

5.10 

2.450 

6.20 

2.95 

7.50 

3.55 

9.00 

Volts 

60000 

70000 

80000 

90000 

100000 

110000 

120000 

130000 

140000 

150000 


Distance 
Inches.  Centimeter 


4.65 

5.85 

7.10 

8.35 

9.60 

10.75 

11.85 

12.95 

13.95 

15.00 


11.8 
14.9 
18.0 
21.2 
24.4 
27.3 
30.1 
32.9 
35.4 
38.1 


No.  of 
WIRE' 
B  &  S 
Gauge 

No.  26 

No.  28 

No.  24 

*No.  26 

*No.  24 

*No.  22 

*No.  22 

No.  20 

No.  20 


Diameter 

of 

wood 
CORE 

2" 
2" 
3" 

3" 
4" 
5" 
6" 
7" 


TUNING  COIL  DATA. 


Turns  of 
Wire  per 
1  in.  of 
Winding 

58 
73 
46 
58 
46 
37 
37 
30 
30 


Wave 

Feet  of 

length  in 

Wire  per 

meters  per 

1  in.  of 

1  in.  of 

Winding 

Winding 

30 

37 

38 

46 

36 

44 

46 

56 

48 

59 

49 

60 

58 

70 

55 

67 

63 

77 

No.  of 

Length 

Wave 

Wire  on 

of 

length  in 

Loose 

Primary 

Meters  of 

Coupler 

and 

Loose 

Secondary 

Secondary 

Coupler 

" 

36 

4" 

700 

32 

5" 

800 

32 

6" 

1000 

32 

6" 

1200 

NOTES. — To  find  meters  wave  length  of  any  tuning  coil,  multiply  its  length  in 
;nches  by  wave  length  in  meters  per  inch  of  winding. 

The  data  in  this  table  was  compiled  for  WINDINGS  OF  ENAMELED  WIRE 
ONLY. 

*Indicates  windings  suitable  for  loose  coupler  primaries. 

Wave  length  in  meters  in  above  table  equals  length  of  wire  on  coil  in  meters  mul- 
tiplied by  4. 


WIRELESS    COURSE— LESSON    NO.    20  153 


Lesson  Number  Twenty 

The  History  of  The  Development  of  Wireless  Telegraphy. 

1RELESS  telegraphy  is  but  twelve  years  old  in  its  commercial  and  practical 
development,  yet  it  is  surprising  to  learn  that  the  idea  of  electrical  signaling 
without  wires  dates  back  to  the  birth  of  wire  telegraphy. 
In  1838,  Steinheil  of  Munich,  Germany,  following  the  suggestion  given  by  Gauss, 
demonstrated  that  the  earth  could  be  used  for  the  return  circuit  of  a  telegraph  line, 
thus  marking  the  first  step  and  birth  of  wireless  signaling  by  electricity.  It  is  alleged 
that  he  anticipated  at  the  time  that  eventually  the  two  wires  used  in  telegraphy  would 
be  entirely  eliminated,  thereby  leaving  no  metallic  conductor  between  the  'two  stations. 
Following  the  experiments  of  Steinheil,  a  number  of  experimenters  continued  in 
the  same  path  of  study,  but  it  was  not  until  the  latter  part  of  the  nineteenth  cen- 
tury that  actual  progress  was  made  towards  the  much-sought  goal.  The  following 
methods  then  appeared  to  offer  the  means  of  solving  the  wireless  transmission  of 
electricity: — 

(1)  The  conduction   of   the   electric   current   through    moist   earth.     This   method 
was  worked  upon  principally  by   Morse,  the  inventor  of  telegraphy   in   this  country. 

(2)  Electromagnetic  induction  between  two  parallel  metallic  conductors,  a  meth- 
od  suggested  and  largely  experimented   upon   by   Preece,  Trowbridge,   Stevenson  and 
Lodge. 

(3)  A    combination   of  the    two   foregoing  principles,   which    was    developed    into 
the  first  practical  wireless  system  by  Sir  William   Preece,  aided  by   the   British    Postal 
Telegraph    engineers.  i 

(4)  Electrostatic   Induction   between   metallic   conductors,   separated  by  a  greater 
or   less   distance.     This    idea   was   developed    to   a   working   success    by    Edison,    Gilli- 
land,  Phelps  and  W.  Smith,  as  a   means   of  communication   between   moving   trains. 

Of  the  above  mentioned  principles  of  wireless  signaling,  the  only  one  which 
promised  the  possible  solution  of  the  problem  was  that  used  by  Preece,  consisting  of 
the  two  parallel  conductors,  with  the  earth  return.  Even  this  system  was  disappoint- 
ing, from  the  many  difficulties  which  it  presented.  In  the  first  place,  the  two  con- 
ductors had  to  be  as  long  as  the  distance  which  was  to  be  signaled  across.  For 
instance,  if  a  distance  of  two  miles  separated  the  two  stations,  the  wires  had  to 
stretch  for  two  miles  parallel  to  each  other. 


HEINRTCH    RUDOLF   HERTZ. 

In  1888.  Heinrich  Rudolph  Hertz,  a  young  German  scientist,  who  at  the  present 
time  is  recognized  by  all  as  the  real  founder  of  present-day  wireless  telegraphy, 
startled  the  world  by  his  experiments  with  ether  -waves  produced  by  the  discharge 
of  high  tension  currents.  These  waves  have  since  been  named  "Hertzian  waves." 
He  proved  to  a  great  extent  the  theories  of  Maxwell,  an  eminent  scientist  who 
formed  profound  -speculations  and  mathematical  theories  relative  to  electromagnetic 
waves  and  light  waves,  in  1865.  Hertz  demonstrated  the  wonderful  characteristics 
of  these  waves,  the  most  striking  being  the  similarity  between  them  and  light  waves. 
The  premature  death  of  Hertz  in  January,  1894,  robbed  the  world  of  a  student  who 
might  have  become  a  still  more  important  factor  in  the  development  of  wireless 
transmission. 

The  experiments  of  Hertz  set  a  number  of  experimenters  to  work  in  the  different 
countries  between  the  years  1888  and  1895,  all  striving  to  solve  a  suitable  application 
for  these  waves. 

Nikola  Tesla  in  1892  captured  the  attention  of  the  world  with  a  brilliant  series 
of  demonstrations  in  the  application  of  Hertzian  waves  to  wireless  signalling.  Sir 


Copyright  1912  by   E.   I.   Co. 


154  WIRELESS  COURSE— LESSON.  NO.  20 

William  Crookes  who  was  present  at  these  demonstrations  -was  favorably  impressed 
with  the  possibilities  which  ithis  method  offered,  and  wrote  an  article  entitled  "On 
some  possibilities  of  electricity"  in  ithe  Fortnightly  Review  for  February,  1892,  set- 
ting forth  a  vdvid  prophecy  which  has  been  realized  to  a  great  extent  -to-day. 

In  1899,  Professor  D.  E.  Hughes,  the  inventor  of  the  Hughes  microphone,  gave 
a  precise  description  of  the  experiments  he  had  .performed  with  an  .imperfect  contact 
between  iron  and  carbon  for  detecting  Hertzian  •waves.  This  statement  was  recog- 
nized 'by  several  other  eminent  electrical  authorities  whom  he  had  spoken  to  at  the 
time  of  his  firslt  experiments.  In  1879,  he  succeeded  with  the  imperfect  contact  de- 
tector in  hearing  signals  in  a  telephone  receiver  sent  out  by  the  spark  of  an  induction 
coil.  To  the  scientists  who  witnessed  his  experiments  at  the  time  he  suggested  the 
publishing  of  his  discovery,  but  was  discouraged  'by  them,  for  they  termed  the  re- 
sults as  induction  effect  and  not  the  detecting  of  Hertzian  waves.  It  will  therefore 
be  noted  /that  Professor  Hughes  was  perhaps  the  first  discoverer  of  the  telephonic 
means  of  receiving  wireless  signals,  and  which  is  to-day  universally  employed. 

On  Friday,  June  1,  1894,  Sir  Oliver  Lodge  delivered  a  memorial  lecture  to  the 
deceased  Hertz,  in  the  Ro}ral  Institution  in  London.  The  lecture  was  remarkable 
in  many  ways,  setting  forth  new  facts  in  the  experiments  made  with  Hertzian  waves. 
He  employed  a  glass  tube  filled  with  filings  of  metal,  for  the  detection  of  the  waves. 
Another  detector  'consisted  of  two  pieces  of  metal  clamped  together  by  an  adjustable 
pressure.  To  these  devices  he  gave  the  name  of  "coherers."  Upon  the  reception  of 
the  waves,  the  plates  or  filings  came  together,  and  in  all  instances  were  decohered 
by  hand.  The  refraction,  reflection,  depolarization,  and  other  properties  of  the  waves 
were  demonstrated,  as  well  as  the  sending  of  waves  through  a  stone  wall.  This  lec- 
ture served  to  excite  interest  setting  once  more  a  score  of  inventors  on  the  problem, 
but  using  the  correct  principle  for  the  purpose  of  signaling  without  wires. 


SIR    OLIVER    JOSEPH    LODGE.  PROF.  BRANLY. 

One  of  these  scientists,  Professor  S.  S.  Popoff,  professor  in  the  Imperial  Tor- 
pedo School  at  Cronstadt,  Russia,  developed  an  interesting  device  for  detecting  the 
approach  of  thunder  storms  by  recording  the  lightning.  Upon  a  lightning  rod  mast, 
erected  on  top  of  a  building,  he  connected  a  wire  which  ran  to  the  laboratory.  The 
other  connection  was  taken  from_the  water  pipe.  The  apparatus  consisted  of  an 
electromagnet,  the  armature  of  which  was  attached  to  a  Richard  Pen  writing  on  a 
Richard  recording  Cylinder,  making  one  revolution  per  week.  It  was  possible  to 
make  marks  on  the  cylinder  at  each  flash  of  lightning  at  considerable  distances,  and 
the  apparatus  was  so  sensitive,  that  an  electrical  bell  rung  in  the  same  room  as  the 
wireless  set  caused  the  pen  to  register  on  the  cylinder.  Popoff  stated  at  the  time  of 
these  experiments  that  if  a  means  of  forming  electric  waves  similar  to  those  caused  by 
lightning  were  employed,  wireless  signalling  would  be  an  accomplished  fact.  To  Pop- 
off  we  owe  two  points  in  the  development  of  the  wireless  art,  one  of  which  is  that  he 
was  the  first  experimenter  to  use  an  aerial,  which  is  indispensable  for  practical  work 
even  to-day,  and  that  he  recognized  the  possibility  of  applying  wireless  telegraphy  to 
these  experiments. 

It  was  not  until  the  appearance  of  Guglielmo  Marconi,  a  young  Italian  born  at 
Bologna  in  1874,  who  was  working  on  the  commercial  possibilities  of  wireless  teleg- 
raphy, that  the  actual  progress  in  the  art  began. 

Marconi  had  studied  in  the  Leghorn  Technical  School  under  Professor  Rosa,  and 
had  keenly  interested  himself  in  all  that  had  been  done  by  the  earlier  experimenters 
in  wireless  signaling.  At  his  father's  estate  at  the  Villa  Griffone.  near  Bologna,  he 
began  experimenting  in  June,  1895,  with  the  Hertzian  waves.  Before  long  he  aban- 
doned the  Hertzian  form  of  radiator,,  and  instead  connected  a  wire  to  a  metal  plate 
laid  on  the  ground,  and  the  other  wire  to  a  plate  held  on  the  summit  of  a  pole.  This 
method  had  been  used  by  Popoff  but  without  the  knowledge  of  Marconi.  During  the 
latter  part  of  1895,  Marconi  was  able  to  transmit  signals  a  distance  of  about  IVz  miles 
using  poles  about  25  feet  high  and  with  tin  sheets  suspended  on  the  poles.  Before 
this  time  he  had  succeeded  in  improving  the  Branly  coherer,  and  making  it  more 
sensitive.  He  had  also  produced  an  electric  tapping  arrangement  for  decohering 
the  coherer. 


WIRELESS   COURSE— LESSON    NO.   20 


155 


The  apparatus  in  all  consisted  of  a  coherer,  a  decoherer,  a  relay,  and  a  Morse 
printing  instrument,  all  worked  with  battery  cells.  Choke  coils  were  interposed  be- 
tween the  coherer  and  the  relay,  which  greatly  increased  the  efficiency  of  the  re- 
ceiving set.  Across  the  relay  and  other  contacts,  he  placed  shunts,  -thereby  reducing 
the  sparking  to  a  minimum  so  that  it  would  have  little,  if  any,  effect  on  the  sensi- 
tive filings.  All  the  adjustments  were  carefully  made,  and  he  was  thus  able  to  cover 
ranges  far  in  excess  of  the  other  workers,  who  had  failed  ito  consider  the  slight  de- 
tails of  the  individual  parts.  The  transmitting  apparatus  consisted  of  a  spark  gap 
of  huge  proportions  as  compared  with  the  present  type,  on  to  which  ithe  aerial  and 
ground  wires  were  connected.  An  induction  coil  working  on  batteries  was  employed 
for  furnishing  the  high  tension  current  to  form  the  spark.  His  first  spark  gap  con- 


NIKOLA    TKSLA. 

sistted  of  the  ball  discharger  used  by  Professor  Rhigi,  composed  of  four  solid  brass 
balls,  the  two  center  ones  being  separated  by  a  small  space  filled  with  vaseline  oil, 
the  spark  jumping  from  the  two  end  balls  to  the  center  ones  which  again  broke  the 
spark  iin  the  vaseline  mass,  producing  a  high  frequency  spark.  By  pressing  the  key 
at  the  transmitting  end,  a  short  or  long  dash  was  recorded  on  the  paper  tape.  In 
1896,  Marconi  came  to  England,  and  began  to  draw  the  attention  of  the  scientific 
world  towards  his  apparatus. 

In  July,  1896,  he  introduced  his  invention  to  Sir  William  Preece,  on  which  Mar- 
coni had  already  applied  for  a  British  patent  during  the  preceding  June.  Preece 
was  very  favorably  struck  with  Marconi's  apparatus,  and  in  a  subsequent  lecture 
praised  it  highly.  By  1897  Marconi  had  succeeded  in  covering  nearly  9  miles  between 
Penarth  and  Brean  Down,  across  the  Bristol  Channel.  On  the  Salisbury  Plain  he 
covered  four  miles  over  land.  A  6"  coil  was  employed  in  these  tests  for  distances  up 
to  4  miles,  but  a  20"  spark  coil  had  been  used  for  distances  of  greater  length.  Kites 
were  employed  to  raise  the  aerial  wires,  and  though  reflecting  screens  were  used  these 
were  found  to  play  but  little  part  in  the  results.  Up  till  the  present  time  Marconi  had 
not  invented  any  new  apparatus,  but  had  simply  made  improvements  and  had  ar- 
ranged the  apparatus  in  a  new  manner.  In  July,  1897,  Marconi  undertook  demonstra- 
tions for  the  Italian  Government  at  Spezia,  in  Italy,  and  covered  a  distance  of  12 
miles  between  war  ships.  In  April,  1898,  Marconi  was  transmitting  messages  over  14 
miles  using  a  10"  coil  between  Alum  Bay,  in  the  Isle  of  \Yight.  and  Bournemouth, 
England,  the  distance  being  over  the  sea.  A  10"  coil  was  employed,  and  spark  gap 
consisted  of  four  brass  balls  separated  a  slight  distance  apart  in  an  ebonite  frame. 
One  of  the  outer  balls  was  connected  by  a  wire  to  an  insulated  strip  of  wire  netting 
about  120  feet  long,  supported  to  the  top  of  a  mast  120  feet  high.  The  spark  gaps 
were  1/4"  apart.  With  this  apparatus  a  speed  of  15  words  per  minute  could  be  main- 
tained without  difficulty.  Numerous  installations  followed,  some  being  for  light- 
houses and  lightships. 

In  July,  1898,  the  Marconi  system  was  installed  on  the  steamer  "Flying  Huntress" 
to  report  the  results  of  the  yacht  races  at  the  Kingston  Regatta  for  the  Dublin  Em- 
press newspaper.  The  aerial  conductor  of  the  land  station  was  but  40  feet  high,  yet 
messages  were  exchanged  at  distances  varying  from  5  to  20  miles,  without  difficulty. 
His  Majesty,  King  Edward  VII.,  then  the  Prince  of  Wales,  had  injured  his  knee  and 
was  confined  on  board  the  Royal  yacht  "Osborne"  in  Cowes  Bay.  Marconi,  at  the  re- 
quest of  the  Prince,  fitted  the  yacht  with  wireless  apparatus  and  also  at  the  Osborne 
House,  Isle  of  Wight,  and  communication  was  established  between  these  stations  for 
over  three  weeks.  The  shore  mast  was  105  feet  high  and  the  aerial  aboard  the  yacht 


156 


WIRELESS    COURSE— LESSON   NO.  20 


about  83  feet  high.  The  distances  were  small,  but  at  times  trees,  hills  and  other  ob- 
stacles were  interposed  between  the  two  stations  which  did  not  detract  from  the  re- 
sults as  had  been  expected.  The  successes  of  these  tests  led  many  other  stations  to 
be  built  permanently  for  the  Corporation  of  Trinity  House  to  be  used  in  connection 
with  the  lighthouses  and  lightships. 


GUOLIELMO    MARCONI. 

(Courtesy  Co-Operative  Press.) 

After  many  further  improvements  in  his  apparatus,  Marconi  succeeded  in  trans- 
mitting messages  across  the  English  Channel  from  Wimereux,  near  Boulogne  in 
France  to  the  South  Foreland  Lighthouse  near  Dover  in  England,  on  March  27,  1899 
The  aerial  wires  were  single  stranded  copper  wires  150  feet  long,  insulated  with  india 
rubber,  and  upheld  at  the  top  by  ebonite  rods  as  insulators.  Man}'  scientific  men  were 
present  at  the  tests,  among  which  Professor  Slaby  of  Germany  obtained  his  first  in- 
ception of  what  has  since  developed  into  the  Slaby-Arco  system  of  wireless  telegraphy 

The  first  application  of  wireless  telegraphy  in  saving  human  lives  occurred  when 
the  "R.  F.  Matthews"  on  April  28,  1899,  during  a  dense  fog  ran  into  the  East  Goodwin 
Lightship  and  inflicted  serious  damage.  The  lightship  being  provided  with  Marconi 
apparatus  was  able  to  communicate  at  once  with  the  station  at  South  Foreland  Light- 
house, and  tugs  and  a  lifeboat  were  sent  our  immediately  from  Ramsgate  to  the  as- 
sistance of  the  lightship.  If  it  had  not  been  for  the  speedy  aid  of  the  ships,  it  is 
probable  that  a  serious  loss  of  life  would  have  resulted. 

Many  installations  and  demonstrations  continued,  proving  to  the  public  that 
wireless  telegraphy  was  an  accomplished  fact,  and  was  rapidly  progressing.  A  dis- 
tance of  85  miles  was  covered  between  Wimereux  in  France  and  Chelmsford  in  Eng- 
land, partly  over  land  and  sea.  A  very  important  demonstration  took  place  when 
the  "-New  York  Herald"  employed  Marconi  apparatus  for  reporting  the  results  of  the 


WIRELESS   COURSE— LESSON   NO.   20  157 

International  Cup  race  between  England  and  the  United  States.  Over  4,000  words 
were  sent  in  5  hours'  time,  covering  a  number  of  days.  Another  test  was  in  the 
equipment  of  the  two  cruisers  "Juno"  and  "Europa"  of  the  British  navy,  which  were 
able  to  communicaite  85  miles  without  difficulty.  From  that  time  onwards,  the  in- 
stallations on  land  and  sea  became  so  numerous  that  it  became  an  established  neces- 
sity for  navigation. 

From  1898  till  1901,  Marconi  devoted  himself  to  the  perfection  of  tuned  wireless 
transmission,  which  he  succeeded  in  developing  to  a  working  success  within  that 
time.  His  next  attentions  were  turned  to  transatlantic  wireles*  communication. 

Until  this  time  the  power  used  in  transmitting  had  never  been  over  Vz  kilowatt, 
and  usually  between  200  and  300  watts,  the  transformers  being  10  or  20  inch  spark 
coils.  The  condensers  had  been  ordinary  leyden  jars,  and  likewise  the  telegraph  key 
was  of  the  standard  type  to  break  the  low  amperage  current.  With  the  consideration 
of  greater  ranges,  many  improvements  had  to  be  made  to  handle  the  much  more 
powerful  current. 

A  site  was  selected  at  Poldhu,  on  the  coast  of  Cornwall  and  the  necessary  build- 
ing erected.  20  masts  each  200  feet  high  were  arranged  in  a  circle  upon  which  the 
aerial  wires  were  supported,  being  all  bunched  together  at  the  lower  end  and  enter- 
ing into  the  station.  In  November,  1901,  Marconi  left  England  for  Newfoundland 
with  his  assistants  and  apparatus.  Arriving  at  St.  Johns  in  Newfoundland  on  De- 
cember 5th,  he  prepared  the  apparatus  for  the  reception  of  the  signals.  On  Decem- 
ber 9th,  he  cabled  to  the  Poldhu  assistants  to  begin  sending  the  signal  letter  "S"  from 
3  p.  rh.  to  6  p.  m.  each  day.  After  some  difficulty  in  raising  the  balloons  and  kites, 
he  succeeded  in  receiving  the  signals  on  December  12,  1901,  marking  the  first  bridg- 
ing of  the  Atlantic  Ocean  by  means  of  wireless  telegraphy.  The  actual  power  em- 
ployed at  Poldhu  for  transmitting  during  these  tests  did  not  exceed  10  to  12  kilo- 
watts. The  distance  covered  was  approximately  2,200  miles.  At  the  receiving  end 
an  auto  coherer  consisting  of  carbon-mercury-iron  in  a  glass  tube  had  been  employed 
in  connection  with  a  telephone  receiver  and  battery.  No  tuning  device  was  employed. 
and  it  is  remarkable  that  the  distance  should  have  been  covered  with  this  crude  ap- 
paratus. 

From  that  time  many  improvements  continued  to  be  made  by  Marconi  until  to- 
day the  majority  of  transatlantic  liners  employ  hrs  apparatus,  and  transatlantic  wire- 
less telegraphy  is  firmly  established  and  being  used  for  both  commercial  work  and 
press  messages. 

While  Marconi  may  be  justly  considered  the  foremost  wireless  inventor,  many 
others  have  helped  in  the  lesser  details  to  make  the  art  a  commercial  success. 

Sir  Oliver  Lodge  who  had  performed  experiments  and  researches  in  Hertzian 
waves  before  Marconi  entered  the  field,  continued  his  work,  and  after  Marconi's 
successful  application  of  Hertzian  waves  to  commercial  purposes.  Lodge  united  with 
Dr.  A.  Muirhead  to  develop  a  new  system.  Following  the  ideas  of  Marconi,  they 
developed  a  very  successful  system,  employing  an  aerial  and  ground  capacity  for  both 
sending  and  receiving.  The  sending  apparatus  consisted  of  the  standard  spark  gap 
furnished  with  high  tension  current  from  an  induction  coil.  The  receiving  apparatus 
consisted  of  a  mercury  coherer,  an  entirely  new  departure  from  the  Marconi  filings 
coherer.  This  detector  consisted  of  a  small  steel  wheel  dipping  into  a  drop  of  mercury 
held  in  a  rubber  cup.  The  contact  'between  the  wheel  and  the  mercury  was  normally 
separated  by  the  film  of  oil  spread  over  the  mercury,  but  under  the  influence  of  the 
Hertzian  waves  the  two  conductors  came  together,  bridging  the  circuit  for  a  relay, 
which  in  turn  closed  the  writing  register.  The  Lodge-Muirhead  system  became  one 
of  the  best,  and  to-day  is  still  recognized  as  an  improvement  over  many. 

Dr.  Adolf  Slaby,  one  of  the  engineering  professors  in  the  Technical  High  Schools 
at  Charlottenburg — Berlin,  had  been  industriously  working  on  the  problem  of  wireless 
telegraphy  prior  to  Marconi's  success.  His  attention  was  called  to  the  experiments 
of  Marconi,  and  he  visited  the  young  inventor  to  witness  the  cross-channel  tests.  Slaby 
being  a  deep  scientist  thoroughly  studied  Marconi's  apparatus,  and  noted  the  many 
improvements  which  he  afterwards  incorporated  in  his  system.  He  joined  forces 
with  a  young  student  and  electrical  engineer,  Count  Von  Arco,  who  developed  the 
Slaby-Arco  system  which  remained  standard  until  recently,  being  replaced  by  the 
more  modern  systems.  The  Slaby-Arco  apparatus  utilized  the  same  principles  as 
Marconi,  employing  an  induction  coil  working  on  lighting  current  with  a  mercury 
interrupter,  and  the  standard  spark  gap  and  leyden  jars.  The  receiving  set  con- 
sisted of  the  silver  filings  coherer,  and  the  relay  with  the  Morse  register. 

Professor  Ferdinand  Braun  of  the  University  of  Strassburg,  also  contributed 
largely  to  the  advancement  of  wireless  telegraphy,  though  is  not  as  well  known  as 
other  less  capable  investigators  and  inventors.  As  early  as  1899,  the  German  patent 
office  granted  patent  rights  to  Braun  on  closed  oscillating  systems  with  an  inductive 
coupled  antenna.  This  system  was  advocated  by  Braun  as  possessing  remarkable 
efficiency  over  directly  coupled  systems  employed  by  other  rival  systems.  Braun  be- 
came associated  with  the  firm  of  Siemens  &  Halske,  so  that  his  apparatus  might  be 
manufactured  and  placed  for  sale.  His  final  and  commercial  sets  consisted  of  a 
large  coil  worked  with  an  electrolytic  interrupter,  a  set  of  leyden  jars,  enclosed 
spark-gap,  oscillation  transformer  wound  with  insulated  wire  placed  in  oil,  and  for  the 
receiving  set  the  standard  type  of  coherer,  relay,  and  Morse  register.  The  coherer 
consisted  of  a  glass  tube  containing  polished  steel  plugs  with  steel  filings  between 


158 


WIRELESS   COURSE— LESSON   NO.   20 


them.  An  aerial  connection  was  utilized,  but  instead  of  using  a  ground,  the  capacity 
method  was  employed.  This  consisted  of  two  metal  tubes,  one  fitting  within  the 
other,  so  that  it  might  be  drawn  out,  making  more  or  less  capacity  with  the  earth.  A 
number  of  these  "balancing  capacities"  could  be  used  in  accordance  with  the  require- 
ments of  the  station.  In  the  summers  of  1899  and  1900,  Braun  established  communi- 
cation between  Cuxhaven  and  Heligoland,  a  distance  of  40  miles,  using  aerial  wares 
90  feet  high,  and  the  inductive  coupled  antenna  connection  for  transmitting  contrary 
to  the  other  systems  at  the  time. 

In  the  summer  of  1903,  the  inventions  and  interests  of  Slaby,  Von  Arco,  Braun, 
and  Siemens,  were  combined  and  a  single  company  formed  bearing  the  name  of 
"Gesells'chaft  fur  Drahtlose  Telegraphic"  and  operating  a  system  known  as  the  "Tele- 
funken"  system.  This  system  has  been  rapidly  developed,  and  presents  to-day  per- 
haps the  acme  of  wireless  telegraphy  perfection,  a  description  of  which  will  be  found 
under  the  heading  of  "Quenched  sparks"  in  a  previous  lesson. 

Professor  J.  A.  Fleming  has  made  many  valuable  contributions  to  the  steady 
advance  in  wireless  telegraphy.  Among  his  most  important  inventions  is  the  Fleming 
wave-meter,  which  was  among  the  first  to  be  introduced  in  the  art.  The  audion, 
which  is  also  known  as  the  "Fleming  Oscillation  Valve"  is  likewise  an  invention  of 
Fleming,  though  Edison  and  other  workers  had  noticed  and  suggested  upon  the 
possibilities  of  the  peculiar  phenomena  of  a  heated  vacuum  in  other  directions.  Many 
other  inventions  are  credited  to  Fleming,  and  while  of  considerable  importance,  our 
space  does  not  permit  a  full  account  of  these. 


LEE    DE    FOREST. 

(Courtesy   Co-Operative    Press.) 

Dr.  Lee  de  Forest  is  another  American  worker  in  the  wireless  field,  who  has  in- 
vented numberless  improvements  in  the  art.  He  founded  the  De  Forest  Wireless 
Company  which  was  later  taken  over  by  the  United  Wireless-  Company,*  which  till 
recently  remained  the  largest  company  in  America,  and  operated  over  a  greater  field 
than  any  company  with  the  exception  of  the  Marconi  interests.  Dr.  De  Forest  has 
turned  his  attention  to  Wireless  telephony  in  the  last  few  years,  and  has  accomplished 
some  results  in  that  direction,  and  is  now  connected  with  the  Federal  Telegraph  Co. 

*The  U.  W.  T.  Co..  is  now  owned  by  the  Marconi  Wireless  Telegraph  Co. 


WIRELESS   COURSE— LESSON   NO.   20 


159 


In  America,  Prof.  R.  A.  Fessenden  began  experimenting  in  1899  while  in  the  em- 
ploy of  the  United  States  Weather  Bureau  at  Washington.  Among  Fessenden's 
numerous  inventions  are:  the  Compressed  air  condenser,  the  hot-wire  barretter, 
which  consisted  of  a  minute  piece  of  platinum  sealed  in  a  vacuum  bulb.  Fessenden 
is  given  credit  for  having  invented  the  electrolytic  detector,  which  was  for  a  num- 
ber of  years  the  standard  of  detectors.  By  constant  application  to  experimenting  and 
study  he  has  perfected  a  system  which  is  largely  employed  and  found  to  be  exceed- 
ingly powerful  for  long  distance  ranges. 

Dr.  John  Stone,  and  H.  Shoemaker  are  other  prominent  American  inventors,  both 
of  whom  have  developed  successful  commercial  systems  bearing  their  names.  At  the 
present  time  both  of  these  workers  have  retired  from  the  active  wireless  enterprises, 
though  their  systems  are  largely  employed  on  various  ships  and  in  land  stations. 

In  Europe  we  must  not  forget  to  remember  other  eminent  workers  but  of  less 
renown.  Blondel  in  France  made  many  suggestions  and  improvements  in  selective 
signaling  which  are  being  used  to-day,  as  well  as  other  discoveries.  Schloemilch  and 
Ferric,  of  Germany  and  France  respectively,  both  discovered  the  electrolytic  detector 
independently,  which  was  afterwards  patented  by  Fessenden  in  the  United  States. 
Both  of  these  workers  have  perfected  other  valuable  apparatus  which  are  being  used 
to-day. 

Wein  and  Goldschmidt  of  Germany  have  produced  valuable  inventions.  The 
former  is  the  originator  of  the  "Quenched  Spark"  method  of  wireless  signaling 
which  is  an  entirely  new  departure  from  the  Marconi  spark  system  that  had  been 
used  for  years  and  still  to-day  is  the  most  universally  employed.  The  latter  has  per- 
fected a  high  frequency  alternator  which  has  a  sufficient  output  and  efficiency  to 
make  it  a  success  when  used  in  connection  with  wireless  telegraphy  and  telephony. 
Perhaps  the  future  contains  many  surprises  through  the  correct  application  of  this 
high  frequency  alternator. 


HUGO  GERNSBACK. 

Valdemar  Poulsen  of  Denmark,  has  spent  many  years  in  the  study  of  the  elec- 
tric arc  method  of  transmitting,  and  his  system  is  being  successfully  exploited  in 
the  United  States  to-day  by  the  Federal  Telegraph  Co.  It  possesses  wonderful  tun- 
ing merits,  and  long  ranges  with  the  minimum  power  consumption.  Von  Lepel,  a 
German  scientist,  has  likewise  perfected  a  system  employing  a  new  principle,  of 
two  metal  conductors  separated  by  a  thin  piece  of  paper  which  has  a  hole  cut  through 
its  center.  This  system  has  been  found  to  work  advantageously  for  military  pur- 
poses, for  it  also  possesses  an  unusual  degree  of  selectivity  which  cannot  be  obtained 
with  most  spark  systems. 


160  WIRELESS   COURSE— LESSON   NO.  20 

Through  the  amalgamation  of  the  ideas  and  experiments  of  the  many  eminent 
scientists  and  others  of  less  note,  the  present  w.ireless  industry  of  to-day  has  been 
evolved,  covering  a  period  of  about  12  years  in  actual  advancement  from  its  first 
practical  demonstration.  To-day  every  vessel  of  a  reasonable  size  carrying  a  certain 
number  of  passengers  .is  required  to  possess  wiireless  equipment.  The  industry  em- 
ploys numberless  men  who  are  especially  trained  for  the  positions  and  pass  a  Govern- 
ment examination  before  being  entitled  to  positions. 

Amateur  wireless  telegraphy  has  advanced  rapidly  in  the  United  States.  In 
1905  there  were  possibly  a  handful  of  experimenters,  and  whom  could  receive  a  sig- 
nal or  two  on  a  crude  coherer  device  which  was  home  made.  Expensive  apparatus 
could  be  bought,  but  at  prices  far  beyond  the  reach  of  the  greater  number  of  enthu- 
siasts. These  expensive  sets  ait  the  most  were  impractical,  and  only  serviceable 
for  a  demonstration  in  the  lecture  room.  In  1904  Hugo  Gernsback  founded  the 
Electro  Importing  Company,  which  had  for  its  main  object  the  supplying  of  amateur 
wants.  He  'began  the  designing  of  a  coherer  set  with  a  1  inch  coil  which  could  be 
used  for  ranges  up  to  one  mile.  This  apparatus  was  followed  by  a  tuning  coil,  then 
by  a  different  type  of  detector,  and  by  thus  adding  a  new  instrument  from  time 
to  time  to  the  ever  increasing  stock,  the  Electro  Importing  Company  offers  to  the 
experimenters  at  the  present  time  a  complete  wi-reless  equipment  equal  to  the  best 
of  commercial  sets  within  the  reach  of  all.  Gernsback  has  developed  hi'S  apparatus 
with  great  difficulty,  having  many  obstacles  to  overcome.  It  would  have  been  an 
easy  task  to  design  apparatus  which  could  be  sold  at  a  prohibitive  price,  but  to 
manufacture  and  sell  wireless  apparatus  at  a  low  coat  has  proven  a  difficult  problem, 
which  fortunately  to  young  America,  has  been  met  by  Gernsback.  He  also  has 
founded  the  Wireless  Association  of  America,  which  has  been  formed  to  protect 
the  interests  of  the  amateurs  against  unfair  legislation  which  threatened  the  develop- 
ment and  liberty  of  the  youthful  experimenters.  In  1908  Gernsback  founded  the 
now  well  known  periodical  Modern  Electrics,  which  to-day  is  considered  an  author- 
ity on  wireless.  This  periodical  has  helped  perhaps  more  than  anything  else  to  make 
American  amateur  "Wireless"  what  it  is  at  present. 

It  is  doubtful  whether  the  young  experimenters  of  America  appreciate  the  work 
which  has  been  done  for  them  by  Gernsback,  the  originator  of  experimental  wireless 
supply  houses  in  the  United  States. 


CONTENTS. 

Lesson  No.     1 The  Principles  of  Electricity. 

"        "      2 The   Principles  of  Magnetism. 

"        "       3 Dynamos,  Motors,  Generators  and  Wiring. 

"         "       4 The  Principles  of  Wireless  Telegraphy. 

5 The  Amateur  Transmitting  Sets  and  Apparata  (Part  One). 

"        "       6 Transmitting  Sets   (Continued). 

"        "       7 New  Transmitting  Systems. 

"        "      8 Receiving  Apparata   (Part  One). 

9 Receiving  Apparata  (Continued). 

"  10 The  Detectors. 

"  11 Aerials,  The  Wires  of  the  Wireless. 

"  12 The  Hook-Ups  and  Connections  (Part  One). 

"         "  13 The  Hook-Ups  and  Connections  (Continued). 

"  H Operation   of  the   Instruments.     Wireless   Regulations. 

"  15 Learning  to  Operate.— The   Codes.     Wireless   Law. 

"        "  16 Commercial  Ship  and  Land  Wireless  Stations. 

"         "  17 High  Frequency  Currents. 

"        "  18 The  Wireless  Telephone. 

"  19 The  Mathematics  of  Wireless  Telegraphy. 

«  20..  ..The  History  of  the  Development  of  Wireless  Telegraphy 


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